MTN DEBIT ORDER ISSUE

Ever since MTN took over my contract from Nashua Mobile this year I have been having issues with my debit orders. MTN have an issue with their debit collections month after month and keep insisting that the problem is NOT with them when IT IS THEIR ISSUE. I have been inundated with unacceptable SMS notifications from MTN, as well as the inconvenience and humiliation of my line being suspended yesterday. I have been a loyal customer for 15 years and this is the service they provide. MTN system issue to debit my AMERCIAN EXPRESS CARD efficiently is affecting my IMMACULATE credit rating. I end up having to call MTN just about every month to REITERATE that my debit orders have NOT been DECLINED by my BANK there are sufficient funds available. I then request MTN to do a MANUAL collection which never gets done on time, so I end up making payment from my OTHER BANK account so MTN get DOUBLE payment. I want MTN to refund my money for the double payment. I refuse to be subjected to this humiliation as a result of MTN not taking accountability for THEIR DEBIT ORDER ISSUE. I no longer want to keep my cell phone contract with MTN I want to port my cell phone number to another service provider