The Exigent Circumstances is "national emergency" since 1861...

Upon non-response to this demand, I would do a Privacy Act request for the currently-effective signature card on file for the account, including all amendments thereto.

Upon receipt, would record a copy with affidavit in support in county, and get a certified copy back out.

Then mail copies of that to all pertinent parties as needed.

If allonge-amendment is missing from card, then file suit in a court of equity for breach of trust and violation of 12 USC 411, to get a declaratory judgment that the allonge-amendment is effective on the account, using Rod Class's Amended Complaint 2 as a template to start with...