I want to echo a similar issue I'm having. I haven't ever exceeded 100gb/day over the last 2 months (as far back as you can see online). I typically use around 50gb or less per day, and have not exceeded my monthly limit in 10 months of using the service. Yesterday, I get an email saying I'm at 90% of my data usage for the month but that my cycle would be resetting the next day. Coincidentally, the day before the cycle was going to reset, Cox is saying I used 258gb in one day - the equivalent of streaming 4k video for 33 hours - and now I'm over my data limit for the month.
Support suggested someone may be stealing my WiFi (there are no unauthorized devices on my router) and I should reset my password. No way to check which devices are using THAT much data.
Maybe it's a crazy coincidence and a WiFi pirate logged in the day before my cycle reset and used 400% more data than usual, or Cox is artificially inflating the numbers at the end of the month in order to collect "overdraft" data fees. If there's an attorney or other customers interested in investigating this, I would be interested to see what you find.