I suggest contact them immediately to have the charge refunded, let them knowing you will be performing a chargeback if it isn't refunded. If they don't refund, call your credit card company and perform a chargeback. Additionally have the credit card company ensure no additional charges can be made as they aren't authorized.
Regardless of the money it's more the point of the matter, you seemed to have followed their cancellation policy (though their end sounds to have been pretty slow) and you still get charged - pretty frustrating. I know I would be pretty trigger happy for a chargeback, but at least give them a chance to make things right. Hopefully they will make good of the situation!
By the way, the last thing i heard before leaving, and that they also made sure to tell when they asked me if i really still wanted to quit - was that i had the next 2 months free. So i shouldn't been charged this month even if i still used the account.
Really, i just signed up with them... hope they don't do that in the future.
Maybe its just a one off, lets hope so..
I once had a shell account with a company and they had some problems and lost their database or something but i canceled my paypal subscription and they didnt realise for 5 months lol course i didnt tell them either
but it does happen its not always avoidable
its why a company needs a good support system