Bad service and unfair customer treatment

As from the 7/08/2018 my mother Thalitha who has a contract with Cell c discovered that she has been incorrectly debited for the contract. In 2017 she bought new contract where she did substitution of goods because what was delivered its not the phone she wants. Courier service was sent by cell c to collect and give correct phone. So instead of administration cancelling and updating her records as returned goods with substitution thy kept both contract open debiting monthly for are year now. So we informed the customer service thy saw the flaws on their thy kept saying thy will refund her but tht has not happen since the 7/08/2018' when she calls 084 contact line thy keep promising to call back but thy don't. Its unfair for consumer to suffer to such an extent to get what is rightfully hers. Ref num for incident is: ********** 0555....my mum num is ********** 813