Chase IPN

Earlier this year we sent Chase "a Chase rubber stamped" IPN to cover the mortgage debt. They signed for it and stamped it "RECEIVED JUL 26 2018 PAYOFF DEPT." Then Chase sent back that original IPN to us. We waited in excess of the 90 days to have them clear their books of the debt. While we have been waiting we honorably made payments with full confidence any "overages" would be reimbursed after the process was completed. The debt still remains on their books. Before I address this issue is there anything we need to know? I want our response to clear, concise, accurate. I have my own thoughts but I am wanting to hear others experience. Thank you,

Jericho