MDB - Refusing settlement offer and loading account with charges

MBD informed me in 2021 that they bought my credit card debt from Std Bank (I had an active and up to date payment arrangement at the time). To date (4yrs) I have paid R32,500 on a R48,000 debt and the current balance on the MBD Statement is still just short of R30,000. I've request detailed statements of accounts several times in the past, telephonically and on email and they never respond. Last month I offered a 60% full and final settlement of the debt and they rejected, saying I don't "qualify" for discount but can't give me a reason why or what the "qualifying criteria" is. Surely this is *******? I can't afford the monthly installment anymore and wanted to settle the debt, but they refuse ??? Well, now they're not getting anything. I'm done paying.