CM400 Modem high data use with nothing plugged in

I have a cm400 modem and a netgear router not sure of its model right now.  In the past 3 days my isp says i used over 400gb of bandwidth and I wasnt even home, the only thing that was one and connected to the network was a wemo switch.  I unplugged my router yesterday and just left the modem plugged in with nothing connected to it and they still show that I have used 47gb of bandwidth since i unplegged the router.  So does anybody have any idea why my modem is requested and pulling down so much data by itself? any help would be appriciated as they have already capped my speed for the month and at this rate it wont take long for them to cap it next month.