Incorrect debit order again.

I am really unimpressed by the stop debit order that was put on my account for MTN as they try to debit the incorrect amount from my account without stopping their absurd nonsense. I was told by the FNB operator I spoke to 2 weeks ago that MTN won't be able to debit from my account again as I prefer to pay per QR code on my account mailed to me as my mother-in-law was de*****ed by almost 16k from MTN. Now MTN tried to debit *the total incorrect amount* from my FNB account twice which causes me to incur bank costs I can not afford. FNB always wants to know how can you help? Please give me the good service I have received previously as I have requested MTN to not be able to debit from my bank account. I am awaiting feedback in this regard. Thank you