Dissatisfied MTN services

I am extremely dissatisfied with MTN, I have switched banks recently and also informed MTN that my banking details have changed so that my debit order can go off on the correct account, after receiving confirmation that my account details have been updated my debit order is still going off on the wrong account causing me to pay a substantial amount of bank charges as there are no funds in my old account. I have sent 4 emails to the customer care of MTN so that they will refund me the bank charges and I have received no reply I have called them multiple times and no one can assist me I have even been to the MTN branch and they keep telling me to call the number. I am fed up and I don't know what to do, please can you help me.