Cell c trying to get more money than what was owed

During covid 19 cell c stopped our cellphone contract and refused to accept my wifes no work no pay paperwork. We have been paying back that debt through debt review and recieved the statements from our lawers that the outstanding amount is paid off. Today we get an sms from cell c lawers stating we still owe them over 4000 rand. This is bordering on ***** as we paid off our account. We tried phoning cell c lawers but we cant get through to them. I will never recommend this company to anyone. Worst cellphone network out there.