Don't stew and get bitter over things that you can't control. Corollary: Don't assume it's ageism when you don't have proof and can't do anything about it anyhow.

More often than not, companies are not serious about hiring, or they are simply fulfilling an interview-to-hire ratio. They are going to behave badly throughout the interview process and sabotage themselves and you over dumb things - even dumber things than ageism. Hiring is absolutely the worst aspect of the tech business, rife with incompetence and lies.

You have to move on and keep hammering away anyhow. Hang in there.