Worst service provider ever.

The service is pathetic. I had a contact with Cell c which I no longer required then I paid the account up on the 12 February. On the 14 February I received a paid up letter but now whenever I want to apply for credit it shows I have been listed on ITC by Cell c. I have tried to contact them and no one is willing to help. This is not acceptable as I don't owe them a cent and they are ruining my name. This is the worst service provider I have ever dealt with. I even have proof of the letter. I am very disgusted. I need my name to be cleared as it been 5 months now and they are failing to sort this mess.