FNB Charging huge interest on Loan they have handed over and refused to help me pay back to them

I had a loan with FNB that I failed to pay for some time. After getting back on my feet I went back to pay it but it had already been handed over. I made an arrangement with GL Attorneys and I've been paying for 10 months now. I have paid over R17000 now over that period of 10 months but the debt is not going down. It's still on the same range I started paying at. I have enquired with FNB and they said since the account has been handed over there's nothing they can do. When I call their attorneys they say FNB adds interest to my loan account and there's nothing they can do as well as it's up to FNB. My R17000 went down the drain and the loan is still over R43k. When I check the account FNB charges me an interest that is over 80% of my money repayment. They are leaving me with no other option now than to let them blacklist me for good which I was avoiding. R17000 is a lot of money for me to pay a loan that will never end. I don't understand how FNB is still adding that much interest on the account they have handed over and refused to handle. I had went to plead with FNB to take back the account if possible and let me pay them directly so that my loan can finish and they refused but I'm still charged that much and paying with no difference. I feel like I'm being ****med now