Almost the same story about cancelling with A2B2/CheapVPS. I submitted cancellation, and they said that my account will be cancelled. Then after a week, I still receive an invoice. I submit a ticket saying that I cancelled already. After a week or so, they contacted me manually saying that the invoice is still due. I check the ticket and no reply. I decided to wait a bit because it was new year after all. A week has past, and this time, they had this another manual notice saying that I still owe them money and that I should pay up ASAP. By then, I've gotten really pissed, and threatnened that if they do not solve it by 2 days, I will post here.
Guess what? 4 hours later, my account was cancelled. I guess you can't be always nice when dealing with these things.