Sudden huge increase in internet data usage

Without any change to my family's pattern of usage or number of devices, our account's data usage has skyrocketed. Some how between yesterday and today my account has used over 300gb of data, almost 100gb of which was in the middle of the night last night while my family was all asleep! I awoke to 2 text messages this morning saying that hit 90% and 100% without me doing a single thing.

I spoke to 4 different agents on the phone. The last one tried to blame my modem/router (a 3-5 years old Motorola) and said there could be "leakage" as if my modem could have "leaked" 100gb in just 3 hours.  She asked me to hang up and call Motorola and ask them  if they knew what was happening! Why would Motorola know a single thing about my data usage, all they did was make the device! I was hung up on by the agent with-in 5 minutes of the conversation starting. I have over 10 years in IT, this makes no sense.

The worst thing is, I am still getting conflicting reports from Xfinity themselves as to how much data I've used. The text messages said I was at 100% for the current month as of this morning. The first agent said I hadn't used 10% yet this month. the second agent said I was at 100% The xfinity website chat bot agent has at one point said I had used 100% and then later today 0%. The xfinity app on my phone eariler today also said 100% but at the moment says I've used 0% for the month. I have no idea how much data I've actually used and at this point I can't trust any number out of xfinity to be accurate. Horrible customer service. Seriously considering moving to AT&T.

[Edited: "Solicitation"]. I switched and magically my usage returned to normal. Higher speeds, lower cost than Xfinity as well.

I am having the same problem. I usually use 200 - 250 a month and in 3 months it’s shot up to over 1.2 Tb. Seems to double every month. Only change is I got a new modem from Comcast 3 months ago

This is crazy the number of people having this problem

Same issue here (‎Usage Spike and it's not my Traffic - Can Anyone Help? | Xfinity Community Forum) and there doesn't seem to be any way to resolve this with Comcast.  I've been a loyal customer for over 20 years, but it may be time to switch :(

EDIT: This appears to be a solution.  For the first 18 days of April, my data usage from Xfinity and the usage reported by my router are very close.

All, I may have figured out a solution, or at least something to try.  I was burning through 100GB+ a day, according to Comcast, but it was actually around 20GB according to my router. Since doing this two days ago, it looks like I'm using ~20GB again, which is correct.  Customer service was utterly useless, but after reading through this or another thread, I saw a guy that said he turned off his modem for three days and that fixed it.  I wondered if a new IP address was all that was needed, so I set off to release and renew my IP.  You used to be able to turn off your modem for 10-30 minutes and it would release the IP, but now it seems that Xfinity locks it to your modem's MAC address, so here's how to do it:

1. Check your IP address first by going to whatismyip.com or a similar site.
2. If you are connected directly to your PC, you can do an ipconfig /release and ipconfig /renew from the command line, then skip to step 4.
3. From a router, you will need to use the "Clone MAC address" tool in your router settings.  Some pull your network card's MAC address, but if not, use ipconfig /all from the command line to see your WiFi or ethernet adapter's MAC address and use that. 
4. You'll need to unplug the modem for 60s after doing this and when you power back up, you should get provisioned with a new IP address. (Note: some routers may need to be power-cycled as well).
5. Go back to the site from step 1 to see if you have a new IP address.

I can't promise this will work for you, or keep working for me for that matter, but it's worth a shot.

Do not listen to the representatives they say the calls are being recorded and monitored that's a lie Comcast makes money from people what they promise verbally and with the right on the screen it's two different things that's how they make their money by lying to people so your phone calls are not being recorded or monitored just think about it I've been with Comcast for almost 25 to 30 years and I got treated like garbage by the representatives and management what's funny they don't have a human resource so you want to put a complaint it stays within themselves nothing but lies

I have the same issue. We usually use around 200GB for the last 5 years, then out of the blue for months now we have been well over 700. I called a talked to at least 3 rep that had no clue as to why. Nothing changed. We don't game. We sometimes watch TV online and just surf the net. They talked me into getting the unlimited but I don't want to keep paying that. They also said they would put a ticket in and someone would call me back. That was 3 months ago. It seems like so many people have this same issue with no solution and they don't seem to care/

Today, at 8:20 am, I received a message I was at 90% usage, so about 1100 GB. At 10:20, I was at 100%. When I logged in a few minutes later, I was at 1800 GB. I was not online, none of my devices were in use. I typically use 200-300 per month. No way I used 800 GB in less than an hour.  I called and was told it was probably my own fault, nothing wrong on the Comcast side, and I just needed to update my password. Maybe it's a bug. They didn't know. I have a Comcast modem. No resolution. I have to wait and see if it continues. 

I have been with xfinity for 20+ years. Last month I exceeded the data limit of 1.2TB, normally my data usage was 400gb to 500gb. This morning (6/1/2003) my data usage was reset to 0, but by the time around noon my data usage was shown 6gb. I did not watch movies, only turned on desktop computer. I have not installed any new programs to the computer, so have no idea where this 6DB data wen to.

I too am having a large increase showing in data used.  I’ve double checked and there’s no evidence of someone stealing my internet. No unknown devices. I believe it’s Xfinity up to something. 

Beginning in May, my data usage doubled from what it had been. Prior to May, I was using 600-700 GB every month. In May, I used 1600 GB. The trend continued in June. The worst part is I was on vacation from May 25 - June 11. I had shut down my computers and streaming devices. Our cell phones and tablets were with us. The only thing connected to the internet was my wireless cameras and wireless switches. Yet, per my router, I was using a consistent 37 GB a day for the time I was not home. The 37 GB per day completely explains the change in my internet usage. I have identified all Mac addresses connected to my router and there is nothing unknown connected. I even replaced my modem with a new one.  No change. I have methodically disconnected all the devices on my network and nothing changes my data usage. I have spent over 10 hours on the phone with Xfinity support and they have no idea what is going on. They only want to sell me unlimited data.

Recently I got a T-Mobile 5G gateway and have been using it for the internet with good success. I am going to cancel my Xfinity this week - both Internet and Cable TV and stay with T-Mobile and get YouTube TV. I have been a loyal Comcast customer for 32 years but that ends now.