Hi Goron,
AOL are the spawn of the devil. BT have uncapped all thier broadband services and now only give "recommendations" on how much you should use it. I have never had a phonecall from them and have waxed 174 and 184Gb in the last 6 months (ul and dl).
If your are approaching 50Gb a month usage quota and not downloading stuff or using a lot of streaming services then i would look deeper into whats running on your PC. I bumped into a bunch of computer geeks on IRC once and found out how easy it is to bot a PC running XP, esp if you dont plug the exploits with windows updates regularly.
Check the tasks that are running on your computer and type thier names into google. eg. rundll32.exe throws up
http://www.liutilities.com/products/wintaskspro/processlibrary/rundll32/ as the top hit. It tells you what it does and turns out to be a kosher service.
My money is on you having an unusual one.. eg we had a bot'd PC at uni that was running smsss.exe (not smss.exe which is kosher). It had 2.5 Gb of p0rn
buried in the windows directory and was sending it round the world on a 100Mbit connection. All of this happened because one of my students thought they would install a "connection accelerator".
Hope this helps
Graeme
Access Cleaning Solutions