False installments on my name after closing my CellC account and receiving confirmation of account closure.

I cancelled and paid up my account in February. Never received my payed up letter, and it was such drama just to get a confirmation of my account being Cancelled. 7 months later I come back to SA from Dubai from vacation trying to apply for a vehicle, to my suprise I couldn't qualify because of my credit rating, when I did a check it came out that Cell C has a installment logged on my credit profile for R3051 which is utterly ridiculous!!! I was under the impression everything is handled and I completely paid all my debt. Not only did they fail to send me my paid up letter. They also recked my credit rating! And has the audacity to tell me to wait 2 business days for documentation. Cell C it's 7 danm months later , please fix your mess.