While Comcast expands its usage based billing (here), questions are raised if its metering system is accurate. One of Comcast's subscribers describes in a YouTube post his exchange with Comcast customer service over exceptionally high data consumption charges by Comcast.
"It all started about three months ago, September 2015, when I got a call out of the blue. It was Comcast informing me I was getting dangerously close to my data cap .. I hung up the phone, looked at the traffic logs built into my router, saw that I was not even close to Comcast’s cap .. November 9th, nighttime, we finally arrive home, and I decide to see what was happening with Comcast meter. It was showing I used 120 gigs of data! .. So I called Comcast the next day, Nov 10th, and was patronizingly informed that “it must be somebody stealing your wifi”. Possible, but highly unlikely. I’m a software developer, Linux kernel contributor, and I take my home security very seriously ..."