MTN's solution is to Ignor a legitimate query

MY MTN contract covering more than 15 years is paid monthly by Debit Order. My bank account records a payment each month.

For many months the Statement reflects an alleged unpaid amount which I have repeatedly queried.

MTN Customer Service has responded at least 3 times by requesting confidential Information which was forwarded the same day. As a reference, a copy of my latest monthly Statement was attached each time the query was repeated.

How do I obtain an explanation and have the problem resolved without further delay?