Okay, so to clear this up a little. You don't really do all that much on the net. Your just a normal joe that surfs to the occasional website here and there. You get and reply or send email. All normal things that shouldn't really put you over the top, correct? lets ask this question that I've seen all to often. Do you use Netflix? Either on your TV thru perhaps Wii or thru some other game console, or thru your computer? If so, watching just one movie (1.75hrs to 2.25hrs) can add as much as 2-5 gigs, depending upon if your streaming normal or HD movies. Here's another question. Do you have a wireless router hooked up to your internet connection? If you answered yes to the first question, most likely your have a wireless hooked up. Now here's the kicker, is that router secured against outside intrusion? Another words, is it password protected? With a really good password? If not, you make have a hitchhiker on your internet connection that is getting free access courteously from your unsecured router. There is one other possibility that you may want to think about if none of the above is not relevant to your situation, is that your computer or one or more on that home network is infected and is acting like a spam or virus server. Get them checked out.
Michael