Cell C, is charging me varying money as they debit alot of varying amounts from the one I signed for on the contract

I am not happy with cell c, as I went to pay out cell c from an account I paid the whole remaining balance, but then now I am still told about the account, where else I know I paid it off, because I since took a new contract when I ask the about the fees of my new contract, I am told varying amounts last month I paid alot of money even now I am still to pay alot of money by the end of the period of my contact I will have paid a whole lot of abnormal cash I don't understand of