Failure to update payment records with credit bureau

Was having a loan account with them that was fully paid and be provided with a paid up letter. A loan has been paid more than 6 months ago, and on December I found out that I'm listed as default by FNB. I went to the branch to find out and was told is a mistake because they forgot to update my details with credit bureau. They called a contact centre from branch and I spoke with different agents without getting any help just to be told a person dealing with such matters is off and will call me to resolve the matter a following day. I have been since waiting from December 18 to date nothing happened. I don't owe FNB anything, I paid the loans in full and received paid up letter. FNB must give me an explanation