Wow, and i thought i was alone, but came across this thread.
Essentially i can report a very similar experience:
* I own my own Modem and Router. Have had no problems except a few years ago when Comcast decided to CHARGE ME for my own Modem, thinking that i was renting it
* Have averaged 250-300GB Usage in my house for the prior 6 months, and even got Comcast Data Usage Escalation team (Philippines team) to read and confirm that
* I got pinged today (mid-morning PST) that i was at 90% of my 1TB cap
* I got pinted at ~2.04PM PST that i had now reached 100% of my 1TB cap
I did support chat w/ Xfinity and was eventually told to contact the Data Usage Escalation team (Philippines team).
Spoke with them, and while she was 'nice enough', she was not able to provide much information to me, aside form saying that I should change my password on my Router.
I'm willing to concede that i will change the WiFI password on my router, but how on this green earth do they think i went from ~300GB average usage over the prior 6 months to OVER 1024GB usage (by the 25th of November, no less)??!??
I feel like a mushroom right now...
Hoping for some clarity here.
Fearing the worst, when returning home i immediately virus-scanned all laptops/desktops in the home. I went on my Router and ID'd every device in the house and that was on the Network. None were found to be an "unwelcome Guest", as Comcast Philippines support team so nicely put.
However, when looking at my Traffic Analyzer on the Network, i found that as i was researching my devices that the very desktop i was using...was gobbling up a good amount of Internet data!
Luckily for Windows 10 users, there's a Data Usage option. For newbies, it's under Settings and then under Network and Internet.
When i looked, at the top line, I saw that I had used 608.57 GB within the last 25 days!!!
I fell out of my chair.
More research said that sometimes Online Drives (DropBox, Google Drive, Amazon Drive, etc.) get "stuck syncing". In my case, it was iCloud. Worst was that i never even got the documents i wanted from iCloud. I logged out of iCloud, and promptly uninstalled the program (both profiles, me and wife). The data usage immediately fell to minimal levels...
TL;DR: Scanned all devices, no bad guys (seemingly) on network using my data. Found out that massive data being used by an Online Drive--iCloud in my case. This Online Drive was stuck syncing. I never got data downloaded, but uninstalling iCloud worked in reducing my data usage immediately.
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