Repair appointment but no parts!

I booked a Genius Bar appointment via the Support app to get my screen replaced, I made the appointment for a day and time when I knew I was going to be close to the store - I haven’t actually been into the area of the store for several years, but I had another appointment nearby so it suited me. My other appointment finished early, so I killed as much time as I could, then went about 30 minutes early to the Apple store. I was politely sent away as there were other people who had appointments before me. Fair enough. I came back on time, only had to wait a couple of minutes and a technician came to see me. I need a new screen. It took less than two minutes.

We don’t have one in stock, we can get one in Five days, can I book you in?

But I’m already booked in. Now. Why don’t you have one in already?

We get a lot of no-shows, so we don’t get less common parts in for older phones like yours.

I am more than a little bit livid, as I’m not likely to be passing this way for another few years, they knew what model of phone I had, so they could have told me this 30 minutes earlier. I’m even prepared to pay the ludicrously high price for the repair. They could have explained that the part wouldn’t be there to fix it on the spot in one of the many pointless text messages they sent about the appointment, so I would have cancelled and not wasted half of my day.

Who can I complain to about this?