MTN terrible service since system change.

I am FED UP with MTN. I have been a loyal customer with them for more than 15 years already and praised their service to all who would listen until NOW. Since they changed their billing system it has been a nightmare. January they cut my line the 17th for payment due the end of the month. Phoned and was advised that if I sign a debit order they will take the money on date specified. Or alternatively I have to phone each month and arrange. Did the debit order specified the 30th of each month. February they deducted on the 17th which was an unpaid as I did not have money in my account. E-mailed again and phoned and was again told the debit was in place for the specified date of the30th. I pleaded that they make notes that money can not be taken before that date. Was assured that it would not happen again. Paid at the end of the month the amount that was agreed. 2 Days later I get SMS that I have to pay the new amount or my line would be suspended. And again phoned. Was told end of the month. AND GUESS WHAT yesterday they deducted the amount due on the debit for the 30th off my bank account AGAIN!!!!!!!! Please can someone advise what am I supposed to do since it seems like MTN do not understand how debits and dates work. Each time I phone or mail I can only speak to a service champion. I NOW DEMAND TO SPEAK TO A MANAGER. The only other alternative if this nonsense is not sorted out is to change to a new network as I am not willing to go through this every month. MTN is now costing me a lot of extra money due to their incompetence.