Debit order chaos!!!

Month THREE of trying to sort out why my accounts debit order is not going off!!! For three months I have been getting a SMS on the 22nd(my payment date) that my account is in arrears. Trying to sort it out is a useless case! No-one has an idea how to fix it. I have been paying via debit order from the same account for 25 years! The service is very unsatisfactory and I will not be renewing my MTN contract when this one expires.