Cannot Cancel Account Supscription Now?

Since patch 4.0 came out the game has been unplayable for me. Before the 4.0 patch my computer ran WoW with little trouble. I used to be able to get a decent frame-rate, fast loading screens with medium graphics settings. Now, 90% of the time I cannot log onto a character or zone into a new zone or instance without enduring a painfully long loading screen (usually 10-15 minutes, but as much as 30), then I often disconnect after that long wait. After numerous attempts I might get the loading screen down to 5 minutes or so and actually be able to load into the game. Even then I get a horrible framerate and lag issues. My frame-rate will be less than 10fps, and I will get periodic spikes every 10 seconds or so where I will get 1 or 2 fps (or less than that) for a couple seconds, then the frame rate will go back up to 7-10 fps for 10 seconds or so, and then spike back to <2 fps. I've had to lower my graphics to the lowest settings just to get this kind of performance. The game is unplayable since I cannot zone into and run instances, BGs, arenas, and other end-game content.

Now its been over a week of not being able to play the game and I refuse to pay for a product that is unusable. I tried to cancel my subscription today and the cancel subscription page seems to be conveniently bugged. After I choose my reasons why I am canceling my subscription, I hit the "yes, cancel it" button at the bottom of the page and it just reloads the account cancellation page without canceling my subscription. I've tried logging out and back into Account Management, and it still shows my subscription as active and I am unable to get past the cancel subscription page while trying to cancel my subscription. Do I have to call my credit card company and request that they block payment to Blizzard?

Finally, my last issue: Frankly, it really pisses me off that you do not prorate the account costs, as my account just auto-renewed itself last wednesday (Nov 13) the day after the 4.0 patch went into effect. I didn't even have the patch completely downloaded at that point to be able to know that the game would not run on my computer, so that I could avoid purchasing game time that I will not be able to use.

Needless to say, this past week as been frustrating on more than one level. I'm sick and tired of watching Blizzard siphon my money from me at $.50/day while staring at frozen loading screens, with nothing I can do about it ( now even more so since I cannot seem to cancel my account).