Refuse to refund overpaid amount and provide paid up letter

On the 29th of July 2019 I called the call centre and requested a settlement amount for the outstanding balance that I had with you as I received an email saying there was a discount offer available for the account. The consultant that I spoke to advised there was a 50% discount offer on the outstanding balance and that if I pay an amount of R1766.72 by the 31st of July 2019 and I can call the following day and close the account and request for the paid up letter. She advised once I receive the paid up letter , I should also provide it to Capitec so they can update my account and profile of ITC.

We made the arrangement and I received an sms confirming the arrangement saying I had till the 1st of August to pay the account and close it. I also had an loan account with African Bank and on the very same day I arranged to settle the account by the 1st of August 2019 to which they also gave me a settlement discount and I had to pay R6515.63 in order to close the account. So when the 31st of July came, I went to my closest Pep store with the easy pay numbers which I usually use to pay the accounts and paid R1767 on your account and R5000 plus R1516 =R6516 to African Bank (or so I thought).I paid the accounts as promised and I called the call centre today to request forward the POP so I can request for the paid up letter and I notice on the receipt the amount I was supposed to pay at African Bank was mistakenly paid to your account and the amount I was supposed to pay on your account was paid at African Bank. The cashier at PEP mixed up the accounts this resulted me in short paying African Bank and overpaying your account.

I am requesting that you assist and urgently refund me the overpaid amount which is R4749 (R6516-R1767=R4749). I was told by Nimble Collectors to wait 3-5 working days as the all amount collected from me was paid over to Capitec bank and that Capitec Bank would be responsible for the refund. I then waited and called Capitec Bank to request for the refund and they advised the funds were paid to Nimble Collections on their bank account and they will have to refund the account. They advised it reflects that I no longer owe them but there is no surplus amount reflecting. For the past 12 days I have been going back and forth between them and no want to refund me back. I about to lose the settlement offer from African Bank as it expires on the 15th of August because I am waiting for the funds to be refunded.