More than 3 years debt sold to third-party MDC and I want Prescribed letter

I had an account with the Fix 2019, when I check my credit record its shows at it was closed from the TFG side but was sold to a third-party MDC which now shows as I last made a payment in December last year which is not true and it's impacting my score. I never received calls from TFG to make payments no letters meaning that you all failed to follow your procedure. The account is more than 3 years can I be assisted with prescribed letter as per the law. I don't appreciate day light *******