Pathetic customer service

I had contracts with cell c which had outstanding balances and cell c handed me over to ssda and they would call me every week to find out when will I be making payment and can I increase the payment amount. I then called the cell c contact centre to ask them if I pay the full amount will they supply me with a paid up letter and clear my credit record and she advised yes. I then made a payment in Oct already and when I called the call centre again they said that they can not supply me with the paid up letter. I must call ssda and when I called ssda they said that they cannot supply me with the letter I must call cell c again. I called cell c over 10 times and they customer service is pathetic because all that they do is escalate or give a different story. I eventually went to the Cresta store the lady said I must send all the information which I did but still nothing has been done. The call centre gives me email address which does not exist. I mean cell c quick to fight for their money but cannot assist when you pay the full amount. I paid a large amount of money so that they can clear my credit record and supply the letter but still nothing. They need to attend to this urgently as the credit record affecting my future