Another update: second feedback form response was that the seat was gone, so they'll offer me a full refund if I call in. I called asking for a refund (there are plenty of seats on alternate routings that same day, so I'm happy to just rebook on a different routing) but the agent on the phone said they can't process my refund over the phone and I need to go through the feedback form to do so.

So round three of the feedback form to ask for a refund, I guess. Sure I could just book the ticket I want in cash for like $150, but at this point I'm committed to seeing this saga through. This is the first time an airline has given me a ticket number and yet that ticket number itself ended up being invalid. Usually once I have a ticket number I had assumed that meant I was good to go.