A follow up:
We enlisted the help from a fellow cruiser (fluent in Spanish) who called Mexico
City on our behalf (he was on the phone
for an hour-and-a-half) and got an email
address. My wife wrote an email
(our Spanish-speaking friend edited it) and we got a reply very quickly.
We returned to the Banjercito, dressed in our best clothes (we even wore shoes!) and armed with all the documentation
we could muster, including copies of the email and notes on the conversation with Mexico
It worked. An hour later we walked out with the old, offending TIP canceled and a new 10-year TIP in our hands.
Fair winds and calm seas.