FNB debits account whenever it feels like it

FNB is really starting to annoy me. I have a personal loan with them that I took quiet some time ago. Due to financial difficulties I have been unable to settle it but make regular small payment. I have an arrangement of R550 a month that I stick to. A few minutes ago FNB debited my account with thrice the agreed amount. How is that? And the worst part is that the account was handed over and I have already made payment through the lawyers. I know that I owe the bank and am working towards settling my account. I recently oppenend a new account and now highly regret it. I would like my money refunded please. It is not in there to make my account pretty.