Sudden HUGE Spike in Data Usage

Been noticing a HUGE spike in data usage with no habit change. For July, Xfinity says I've hit 1TB of my data usage limit in 15 days, while my own modem app is showing my actual usage is 1/3 of the amount Xfinity is showing.

Been on the line waiting for somebody to help me for 40min, still waiting, no luck so far. Think Xfinity is scamming me at this point.

7/16 update:

Spent 1 hour 44 minutes on the phone with their "Customer Security Assurance" team, talking to 3 different agents, finally was able to get a daily breakdown of our usage, which (again) is 3-4 times (on a daily basis) the usage showing in our modem app. After questioning the way they are tracking our usage, we were constantly told to contact our modem manufacturer. So things got nowhere.

7/19 update:

3 days after calling their "Customer Security Assurance" team and getting nowhere, now Xfinity app shows we've used 2TB, that means, between 7/16 and 7/19, despite the fact that we've only worked from home on 7/16 and 7/17, we've consumed another 1TB. RIDICULOUS.

BBB complaint submitted.

7/26 update:

• July 22, 5:07PM, Missed the call from the "agent" who's assigned to my case due to a meeting at work.
• July 22, 5:18PM, I called back, spent 33 minutes on the phone being redirected from level 1 support to level 2, then to level 3, somebody picks up the call saying the agent assigned to my case just left for work, saying he would really like to have this specific agent call me back. I told them to call me back on Friday July 26 after 9am.
• July 26, 9:29AM, didn't hear anything from them, decided to call. Spent 17 minutes on the phone AGAIN being redirected leveling up, being told to wait for the agent to call me by "today". I said I have a meeting starting from 11AM, so call me before that, they said they'll pass along the note.
• July 26, 1:12PM, didn't hear anything, decided to call AGAIN. Spent 29 minutes on the phone ONCE AGAIN being redirected leveling up, STILL being told to wait for the agent to call me by "end of day today". Since I have a meeting at 3PM, I told them to pass along the note of "CALL ME BEFORE 3PM PACIFIC TIME".

At this point, unless I have no life, no nap, no meetings, and constantly hold my phone so I don't miss a damn call from Comcast, I'm NEVER getting any real resolution from this monopoly giant. 

7/26 last update:

After updating both my BBB complaint and this post, I finally got a call back from the agent. The "resolution" that I got was that there was some "errors" calculating the usage that some accounts were impacted for the month of July but should be resolved starting August. I'm keeping an eye on my usage for August at this point.