Good luck, I hope all goes well for you, I'd keep on-top of the Manager/Owner of the place, I hope you get some kind of restitution/satisfaction...
I know it's been said by others, Never leave your car unattended with a strange Tech/Mechanic, keep an eye on them always, if they won't let you, then take it somewhere that will, especially when your dealing with a younger mechanic {I use that term Tech/Mechanic very loosely, more like parts replacers, in allot of these places}, I know all the younger guys aren't like that, but it's a far larger chance of a young guy doing this verses an older respected ASE Certified Tech/Mechanic....
I know I'd be pissed as hell, someone would pay one way or another, I'd get restitution for sure...
This kind of crap is a big part of why, I don't trust anyone to work on my cars, I'll buy books & tools to do it all myself, learn how to do it, no matter how long it takes, because it's cases just like this, but also sometime you have to do, what you have to do... Lessons learned