Don't care attitude with no service what so ever

Good day, this will be my 3rd complaint about the same matter as cell c realy don't care. I cancelled a expired contract and done a final payment towards the account. Its been now 3 weeks and I still have not received conformation of settlement or paid up letter. What els can I do to have this mater resolved as I'm running out off options as numerous mails and phone calls was made with no positive outcome. Last I heard was payment was allucated with no further closure on the matter I want my paid up letter to supply to trans union as I raised a dispute with them as well.