The most pathetic customer service received from MTN

I am completely frustrated with MTN. The most pathetic customer service ever experienced!!! I have requested on numerous occasions that MTN rectify my account by sending a Debicheck mandate to my bank for the correct amount according to the invoice. Due to MTN, my credit report has been negatively impacted as two debit orders are deducted from my bank account, instead of one for the total invoice amount. This payment is therefore rejected on my bank and therefore returned, which reflects as a missed payment.

This has been going on for a few months and every month end I phone MTN to request that it is rectified. I am however not finding any joy with MTN, and their lack of customer service is totally unacceptable.