Cancelled contract but still got billed

I cancelled my contract on the 22/08/2015. I was told that the cancellation takes a calendar month and it will be cancelled on 22/09/2015. On 01/10/2015, my account was debited for the cancelled contract. They are now telling me that the account was only cancelled on 25/09/2015 and the benefit was loaded to the account for October. This is really franstraiting because I conformed to all their instructions and they are now dishonestly debiting my account.