incorrect billing

We were told that once our 24 month contract was up that the device fees fall away and we would pay R99 for the data . Our Contract ended in October and in November we were billed correctly. Then in December telkom decided to change its policy , we approached the store to cancel the contracts and we were refunded the overcharged amount . In January the billed us for the wrong amount again . I'm tired of calling customer services and explaining myself. I did a dispute on the amount that was debited and telkom suspends my devices . Nokuthula a team leader at the customer care center is handling the case and i can never get hold of her , either she is not on duty or busy . I have emailed her and there is still no response.