Cell wants to debit even when our contract is done

I took out a contract with cell c where i was given a faulty sim card i have been paying all these months but never able to get my benefits o made a lot of calls to fix i even went to an extend of going to the store ,Now my contract is done with them i wanted to cancel the contract but cell c being the most horrible network in the world they keep on hanging up lines in my ear and dont want to transfer me to relevant department to cancel what i call the worst contract in the world so that they can still debit me even when am not getting my benefits I truly hate cell c and i would never recommend anybody to make use of