Finchoice Bad service

I have a credit account with Finchoice, they handed the account over to their legal department. The legal department got in touch with me and advised that I qualify for a discounted settlement amount. I took the offer and paid, I sent them the proof of payment. I keep phoning every week from the time I paid (14th November 2020) to follow up on my paid up letter and all I get is we will email it to you. I haven’t received this paid up letter till today. Now I am being contacted by a different company by the Name Nimble collections, saying that my account has been sold to them and I owe the full amount. I told them that I paid this account already via a discounted amount and I’m awaiting paid up letter. They told me that I am awaiting paid up letter they said they know not of such. All I am asking for is for Finchoice to furnish me with my paid up letter and remove the adverse they have put against my name on the Credit bureau. ASAP