That's a lot of devices pulling data, can see how you would bump up against the cap. There is a excellent (but long) thread on the cap, what counts as usage, ways to monitor etc here ( http://forums.xfinity.com/t5/Your-Home-Network/Terabyte-Internet-Data-Usage/td-p/2741624) In short, the only data usage that counts is what Comcast reports and the definition of usage, as far as I know, remains a mystery. You can view what Comcast reports as usage at https://www.xfinity.com/manage-my-account, create a sign in if you don't have one and log in. Go to the devices tab and scoll down to see your current month and the last three months usage.
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