Listed wrongful on credit bureau

Fnb listed my name on credit bureau wrongful, i took out a temporary loan on 29 April 2021, of which i paid in full on the the 15 of June 2021. To my suprise when I logged in my account on Experian i found out that fnb listed the account as in arrears for two months, the same i account i paid in full in less than a month. Ive sent them numerous emails without any help. My credit score drop because of this. What is annoying me the most whenever i call them i will be billed on my account "value added fee" huge amount of money, imagine billed for calls while using my on airtime, and this is their fault The last person i talked apologized and said they will fix before the month end(February)with Transunion. Please advise which steps can i take to get this sorted with fnb

I am very annoyed and disappointed