said by Nitra:None of my PC's are used for gaming or use downloaders of any kind (utorrent is used on my htpc and it's just fb and forums on the others) and the reason I am setup the way I am is so that all in/out traffic gets logged through the router (with the exception of internal traffic, ie streaming from one pc to another or copying files from one pc to another) that is directly connected to the Ebox modem.
For your issue, you might have something running the in background that's creating traffic you're not aware of, some games have P2P stuff built in. It seems if you're running over with amounts like that, it very well may be something generating traffic.
You may have some downloader running, etc.
I would firstly, install a program called DUMeter on all your computers. It will keep track in real time, and see what the computers are generating, see if after a few days, this matches with the Videotron counter.