You still don't get it about the contact. It's a child traveling alone. Should the airline just throw them to the wolves?! Or assume that everything will be ok? No, they should not! The parent paid EXTRA (and many airlines require the unaccompanied minor fee) to ensure the child would arrive as expected. It was their absolute obligation to inform the parents when things changed. Why the hell didn't the chaperone call the parents? If United couldn't find the number, the child certainly knew it!

And it's not just about "someone forgetting to make a phone call". The parents asked for updates and got stone walled by Customer "Service". That was salt in the open, bleeding wound. So yes, it's absolutely deserving.

If the airline doesn't want the trouble with unaccompanied minors - DON'T SELL THEM A TICKET. By taking the parents' money the airline willingly assumed the obligation. What more is there to discuss?