Total Idiots working at Cell C

I have cancelled my cell phone contract with cell c in may 2020, final debit was June 2020. Yet I am being billed for June, I am being billed for August. Yet the sim card has been destroyed, the contract has been cancelled, I am really getting tired of service providers that do not know what the hell is going on in their own companies. If I am billed again I will start legal process and I will make it my mission in life to exploit cell c for the poor service and total disregard for cancellation instructions not followed. I mean I followed protocol, I did not upgrade, I cancelled the contract with 30 Day notification, I accepted that there would still be one debit deduction at end of June 2020. Yet I have to deal with incompetence and having to reverse debits that are legal and not contractual as there is no longer a contract with Cell C.