We have been having the exact same thing happen over the past 4 months. We thought "maybe someone else was using our wifi", but no. It really seems funny that our usage is below 30GB per day, except, starting on the 11th or 12th of the month, exactly 10 days till the end of the billing cycle, our usage spikes to 100-150GB per day and stays that way for 5 or 6 days.
We don't use our internet any differently on those days that usage spiked, than any other days. As a matter of fact, our usage has been minimal on a few of those days, because we were out of town, but they were still spiked. How is that?
How is it that these spikes in usage all happen on the same days every month, since the 1TB data cap was initiated?
To tell you the truth, I think it is Cox padding our usage to make us upgrade to unlimited data for an extra $50/month.
I hope to see a class-action lawsuit.