Adverse/Defaulted Account listing!!!!! for what?? an account that's been paid???

I received a notification from the national credit bureau stating that I have an adverse listing on my name, I immediately called the national credit bureau to find out what was going on with my credit report and they stated that MTN listed me as a Defaulted Account (A default will stay on your credit file for six years from the date of default, regardless of whether you pay off the debt)

MY MTN ACCOUNT IS NOT IN ARREARS OR BLOCKED!!!

I confirmed this 3 times today with the MTN call centre agents.

Someone from the correct department a senior has to contact me today to remove the listing and formally apologize, this is completely unacceptable.