MTN Lack of Interest

Have had a cell for many years and not once have a run out of air time. The last two months this has happened and I suggested to my local MTN franchise that something was wrong. They emailed MTN and the following day received sms "resolved" It wasnt!. Suggested to the franchise that MTN prove my call use by providing an itemised billing report. Only if I agree to a future billing cost will they provide my billing report; in the future, but refuse to provide one to prove the past problem. I find this totally unacceptable and it smacks of"if you dont like it, lumpit"