When you open up Windows Updates, what do you see? Mine looks like this:
Do you have anything in your updates screen? When's the last time it says it checked for updates, or installed anything?
Other than updates, I seriously don't see what else from MS that would be downloading. Especially not on a consistent daily basis.
Just to clarify, we're talking about ONE computer here, connecting via a mobile broadband dongle you attach to it, right? You don't happen to be on a network, with other PCs sharing the internet connection?