FNB refuses to repay my temp loan money they accidently debited after I fully repayed the amount

I took a temporary loan from FNB last year and unfortunately I struggled to pay back for the loan. They handed the account over to GL Inc lawyers and I made an agreement with them to repay the loan every month with R500. I made two payments from December and on February FNB temp loan deducted R1000 from my account. According to my knowledge, the fact that I made arrangements with the lawyers since my account was handed over it meant that FNB temp loan had no right to deduct any money from my account since GL Inc is the one handling my temp account. On this same month FNB further continued to deduct more fund from my cheque account. I went to enquire because I had my debits bounce because everytime I had funds in my cheque account FNB would take all my money and empty my accounts. I went to the bank and they called the lawyers but the lawyers said there was nothing they can do FNB needs to reverse the temp loan amount they took. FNB said they won't be able to reverse any money and that GL Inc should reverse the money back into my account. I am stuck now with a crisis because I need to get back my money and don't know what to do. My temporary loan has been paid for and they need pay me back the funds they took from my account.