Cell c lies and messing up my credit record

I have cancelled a contract with cell c about 3 months ago and then they said I still owe them 3 weeks ago I paid them and asked for a paid-up letter and it wasn't sent , they have not updated credit bureau again which just give me a bad credit record when time again I call the call center sent from pillar to post am told it will be sorted but my ref keeps getting closed even if they have not spoken to me . Cell c will say they called but never do so again here are my numbers ********** 593 and ********** 384