FNB takes no pride in keeping promises

I am a private banking client that took out a loan with FNB, within months into the loan I paid a lump sum in an effort to close it earlier, i recently called them to ask how much to pay to close it, it was debited and I asked for a paid up letter and closed it, They chose to pay back into my account an excess and said I paid more, because I had a letter, I didn't mind , the next month the debited again while in position of a paid up letter, I ignored it and thought it will be paid back, again this month they made another debit, what is going on, why is my paid up letter ignored , FNB is useless and need to be reported to consumer tribunal