Paying for nothing

I have cancelled my contract when i was due for an upgrade but vodacom till now is still debiting me. From the many times that I have cancelled finally in October I was told the matter had been seen to and I will even get refunded for previous amounts I paid..When I called in again I was told theres no records of cancellations and all they wanted to do was force me in taking another contract.Iv been to the store and they have now told me my account is prepaid but they still debiting me