Negligence

I have a JD Group/ Russell's Account that was handed over to Nimble, as I was not able to make payments then. Around May 2023 made contact to Nimble to make a monthly debit order arrangement of R300 as I was noticing the hit on my credit score. The problem that I have with them is that they had put my current outstanding debt of R18 500 and some odds as an installment where as I have R300 monthly payment arrangement. I called them today to ask but the consultant failed to explain as to why, let alone assisting me, saying that it cannot be fixed, I asked why and whose fault is it, but she could not assisted. This is affecting my well being so badly because I get rejected when I seek for credit when there is offers on the credit score check platforms, due to "affordability assessment" compared to my income.