Nimble Collection Services and Jet Stores

My JET STORE account was handed over to NIMBLE COLLECTION SERVICES. I arranged to pay R100.00 monthly from 2021. the balance then was R2736.85. At times I pay twice in a month and sometimes pay R200.00. Last month, my balance was R789.85. Last week Friday I paid R250.00, on Saturday I paid R500.00. My balance as on 19 August 2023 was R126.10. Yesterday (22 August 2023) I called to check how I can settle my account, I was told that my balance is now R662.00. When I asked how it went up, I was told that JET STORES has added R536.85 and I need to call them directly. I was given a back and forth kind of treatment. JET STORES said they know nothing about the money as my account is with NIMBLE, so I have to call Nimble to get the information. Today in the morning, I called Nimble for the 4th time and was told that my balance is now R739.00. Between the 2 parties, none is ready to tell me what the money is for. It seems (from the statement) that almost every time I pay, another amount almost the same as what I paid is added to my balance but they cannot explain what it is for. I asked for a settlement amount and they said R577.35, I paid R580.00 and now when I check my balance online, I see it is now at R876.10. All in all, it seems like from 19 August, my balance went up by R750.00 and nobody is ready to tell me what it is for.