Questionable percentage on settlement

I have a cellphone account that was handed over to NBA and in May 2022 I requested a settlement amount and the quote was around R1270.00 and the outstanding balance was around R3100. I then paid an amount of R500 hoping that it'll reduce the settlement. I called this month and requested a settlement and the quote is around R2500. This is clearly unacceptable. When I asked how come the settlement amount only R100 less from the outstanding balance I was told that the percentage on settlement changes now and then. I really find this as disgusting. It's a robbing process.