Bad Handling of Handed over FNB Loan

They are handling my FNB account that was handed over to them. I wade an agreement with them 10 months ago and I've been paying for that said 10 months. My loan was R43k and a few rands I've paid R17k for the said 10 months but I still owe the same R43k. My debt is not going down and it's accumulation over 80% interest of my monthly repayment. On top of all that I pay on the agreed date and I they pay FNB very late and that increase the debt and interest. I've called several times and all they say is that they will call FNB to stop charging interest and I don't understand how does FNB charge interest when the account has already been handed over. I went to FNB and they said there's nothing they can do because it's now up to GL Attorneys and I can't seem to find a solid solution. They keep on saying they will contact FNB and get back to me everytime I call them