Debit order details change nightmare

Changing banking details with MtN has been a complete nightmare, I requested debit order details to be change from 27/07 as my old account is not in use anymore MTN keeps deducting on a incorrect account what happens is that i am being charged for the unsuccessful payment each time and my ITC in this regards it’s negatively affected this morning MTN deducts again to the incorrect account, I am so angry right now how can almost everyone gets this wrong?