Failure to cancell contract

I have been trying to cancel my contract with Cell C since July, I eventually managed to cancel it on the 23rd of Sep 15. I insisted that they send me a confirmation email that it was cancelled and it was sent, Once month later I am still being billed for that same contract that I cancelled. when I call the call centre to make enquires they put me though a voice prompt advert about housing loans and wedding planners. My bank account was debited on the 28 , 30 and 31 Of September and October respectively.