Unless you are a frequent guest of that hotel (or of the other hotels operated by the owner of that hotel), I would say that the lack of response indicates that the General Manager is no longer interested in negotiating. What you received is what you're getting.

It's passive-aggressive, but I'd guess the GM is hoping that you will not return to the hotel in the future.

You can certainly appeal to Hyatt, but that's probably a waste of time. All of the hotel groups like Hyatt automatically send hotel-related problems to the hotel for resolution. All the hotel will do is tell Hyatt what service recovery they already provided. Hyatt will not overrule the hotel and provide more compensation unless a policy was violated or a life-safety issue was present. (And it doesn't seem like either of those things happened here.)