Bad service

I have been trying to get a paid up letter for a account that was settled in December 2021 and not getting any joy. My credit card account was handed over to Nimble collection and I then asked for a settlement amount, I was then told I qualify for a discount on the account and the amount sent in the settlement letter was the amount I should pay to close the account. After payment the amount brought forward and having proof of payment, I was then advised by Nimble that capitec had handed me over again and there was still an outstanding amount to be paid, before this I had spoken to a capitec agent which advised me that they could not give me a paid up letter because I still have an existing loan with them and they can only close the credit card once the loan is paid up. My question is, why does the collection company offer a settlement amount and then come back and tell me that there is an outstanding amount after I had paid the full amount which they had sent to me. I have now also settled the balance which I was told I was liable for. I need my credit card closed and I won't a paid up letter.