AOL did that this to me about 8 years ago....

I had an account with them, did not like thier service at all, left alot to be desired... and consistantly in the 6 month period I had service with them, they double billed me for thier service, and then would not correct the error and credit the extra money (which was a good amount) back into my checking account while lying to me saying that they would or were in the process of doing so, so I called them and canceled. After canceling, about 3 months down the road I got a nasty letter from them, probably about the same as you recently got from them, it also told me my account was going to be suspended/disconnected. SO I called them, they had no record that I ever canceled my account, called me a liar pretty much and treated me like crud... in the end I filed a complaint with my bank over the double billing and never saw that back. At some point I wrote them off and all the cash I had lost to AOL due to thier poor business practices, they certainly have a habit of trying to gobble up as much money from ppl for thier sub standard service and poor customer service skills

As you can see, I think AOL is EVIL....

I can certainly feel sympathy for you in your situation.