Destroying my credit score while they have paid up later and other proof.

I had a loan with Wonga which I settled at the end of November 2023... But Wonga in December 2023 sold the account to nimble for collections. problem is I have given nimble the paid up letter and my latest credit report that proves that I did pay up the loan and it's closed. but they are forcing me to pay them still. They say the bought the account from Wonga so they have to get their money back... But now at the moment they messing with my credit score since they make it seems as if I haven't paid my account for +90 days... I do not understand why they do not deal with wonga direct, since it's wonga that sold them a paid up account not me. Whenever I call the Nimble group to address the matter, they just give me the same response of 'They have escalated the matter'...