MTN fails to update banking details

I have submitted my new banking details to MTN 4 months ago while preparing to close my old bank account. On numerous occasions I got false confirmation from MTN that my banking details have been updated successfully. However, MTN kept om deducting money from my old bank account. The moment that my old bank account closed, MTN was very quick to send me notifications that I hadn’t paid my monthly bill. The mistake is completely on MTN’s side, due to their pathetic administrative abilities. Though, MTN threatens to disconnect me when MTN wrongfully tried deducting money from my old account.