I keep going over my T-mobile broadband allowance - and don't know why

Lally

Oh, I just use it for email, shopping, reading newspapers and magazines. I look at youtube once in a blue moon and don't download any music or anything.

andy2004

Turn off automatic updates,
Turn off antivirus updates, change from automatic to manual, avast is like kaspersky it updates itself every 3-4 hrs, so about 6 times a day.
Turn on WEP on you wireless connection. someone else could be using your connection, if you dont have it password protected.

Download malwarebytes, install, update and run a scan, post log file here. size including updates, about 5mb
before running malwarebytes disable antivirus, usually right click the icon in the taskbar, disable, turn it back on after malwarebytes is finished.
This will tell us if you have any spyware running in the background which could be downloading stuff in the background.
2gb limit is rubbish for most of the internet these days, i download an average of 4gb per day.
other options to save internet usage.
firefox + adblock plus + noscript, and disable flash content, most online magazine use flash and this is probably where your limit is going.
2gb is 2048mb, most flash files can be 4mb+ in size if not bigger.