I also have issues with them proving traffic.
My parents have a 2mbps ADSL through them and they somehow manage to download over 600GB per month. i can assure you they aren't downloading torrents or anything major. they literally use it for emails and my brother plays online from time to time.
I ask how it is possible and they can't tell me.
It is an uncapped account so it not a major issue but still it would be nice to know where all the traffic is being generated.
If i calculate how much data you can download with a 2mbps line i come to around +/- 550GB so they would have to be maxing out the line 24/7 for the month and somehow get a boost every now and then to achieve the reported 600+ MB.
checked the 4 machine for malware, spyware, viruses and no issues there.
busy setting up a firewall for them so i can provide proof that the traffic isn't being generated by them.