Unauthorised debits

My contract ended with Cell C in September with my account paid up to date. I contacted Cell C to inform them that I would not be renewing my contract with them and I was told that I need to give one month notice in order for them to cancel the contract. I asked what did the notice period apply to as the contract had already ended after the agreed 24-month period. I made it clear that I would not be renewing my contract with them and to date my account is still being debited. Cell C, explain to me why you are debiting my account when our agreement ended in September. My next stop is the Ombudsman. I am not going to have my credit record tarnished due to your ********* behavior.