Paid up letter

Good day,

Kindly note I have received settlement offer for 90percent discount in the month of May 2025 and agreed to start paying from June to month end of August. I paid off, then I requested the paid-up letter that's when they inform me that the closure on the account has been declined due to multi payments done. After that they promised to share the paid up letter

And the sad part is they no longer responding to my email's and when I call, they keep on saying will reply to me on emails. Unfortunately, till today I never got respond from them. Please assist me further