Wow, tough crowd... I did not ask for advice on how to handle my personal complaint, am happy with the way I dealt with it and with the way it has subsequently been resolved, so I am bemused by people's near-exclusive focus on my that, rather than what caused the situation in the first place.
There was no "physical confrontation" or "mugging" - that is just absurd - and I can assure you that I am no pushover. The fact is that the certificate was not valid at that hotel. By the same principle, do those who have replied so robustly above think that it should have been honoured if expired, from another hotel group, forged or copied, if I had presented an invalid credit card...? Where do you draw the line at forcing staff to honour a mistake?
I really do think that the fault lies with Hyatt for failing to disclose this hidden list of "Resorts" and I am surprised that there has been so little comment on that, for me critical, aspect.