Canceled Cellc Contract, but still get a account?

My Contract with with Cell C ended on 31/08/2017. But i do received a bill for September month? When I inquiry this, I have been told i never canceled my contract. I went to a Cellc Store in May 2017 (when i was able to upgrade) They could not provided me with the Phone i would have liked. So i told them that i would like to cancel the contract because i can get what i want from Vodacom. ( so according to me this contract should be cancelled?) I was contacted twice by Cell C afterwards to tell me about there Promotions. And both times i told them the same story, that i already cancelled the contract due they cant provided me with what i prefer. Today i called the cancellation department - Ref ********** ********** 25 they told me that this contract was only cancelled on 08/09 when i inquired why i was being billed for September. This is very bad service and unprofessionally!