Upload, download, WHAT?

[badger]

I've been with Sympatico for six or seven years now, beginning with dial-up and now on an 'intermediate' plan, fast but not the fastest. I've never had a problem with the service and their technical people are good at untangling me when things go wrong (rare).
I was checking out my most recent credit card bill yesterday (trying to avoid looking too closely at what I pay each month on my vet's Maserati), and the cost is now DOUBLE what it was in January. Monthly payments have been stable, around 35$, give or take a couple of dollars. Last month, 68$ .
Luckily, the person I spoke with in billing survived my tirade and promptly credited me, but he was unable to explain WHY this happened. My habits never change - I read tons of newspapers, go on pets.ca, do a little surfing on special subjects and that is IT. I never download anything - music, video, games (in fact, in most cases I can't do video, probably because I have not been able to download Service Pack 2 for XP, another outstanding problem) but I realize that I am nevertheless downloading without realizing it on some of these sites (as he imperfectly explained).
But given that my habits have not changed one iota, HOW did this happen?