Cell C upgrade cancellation

My cell c data contract was upgradeable, but didnt want to upgrade the number and returned the device back to Cell C and requested that data contract to be cancelled at the end of term. The device has been returned to Cell C in January 2021 and according to me that was completed when consultant contact me just to obtain the RW number of Ram couriers to stop the upgrade and it will be cancelled at end of term. This did not happen and are know billed for the 3rd month for something that i didnt want and returned. I complaibed with Cell C and they keep avoiding the ussue that this must be cancelled. I must know receive an RMa number which they must provide but dont and still no cancellation and still paying.