Ask for a line-item calculation: principal, interest through which date, late charge, foreclosure fee or other charge. Compare it with the KFS, sanction terms and payment history. Do not pay an unexplained amount just to obtain a document; ask the lender to identify the contractual or disclosed basis.
If the amount is valid, settle it and ask for the revised zero-balance ledger. If it is disputed, keep the complaint focused on that charge and continue paying only what remains legitimately due under the account.