StartingEarly, you obviously know enough to be able to catch them on something like this, and bravo for doing it (even though you kinda expected it would happen, that's no excuse for their behavior). The worse part of it isn't that they made a mistake (happens to the best of us), but that they wouldn't admit to it and treated you condescendingly.
I'm a guy, but I don't know as much as you about auto mechanics, though I know the very basics - I feel confident doing anything up to and including changing my own oil, that's about it. Computers were my first love, and I devoted all my time to it and never did the car thing, though my dad and brothers were big into it. (Dad worked for Ford most of his life).
And I wanna thank you for standing up to them this far. People need to get called out on shit. ESPECIALLY if it's a safety issue - but even if it's not, even if it's just a matter of general principle, they need to get called out. And it doesn't happen often enough. This is just like a situation where someone cuts in line, and will anyone say anything? Usually not. But sometimes there's somebody who won't put up with shit like that and calls them out. Every single person in that line is silently thanking that person for having the balls to actually stand up to someone doing something stupid and/or rude. So THANK YOU. (And it's really awesome when that someone who calls them out is like a 6 foot 4 250lb dude or something, and the offender turns around and is is like CRAP and gets all meek and apologetic, LOL)
A lot of us get taken by bad mechanic shops.
But I wouldn't pursue it any further than you already have. At this point everyone who can learn anything from it has already learned it, the rest aren't gonna learn shit and escalating further has no possible gain it could only turn out neutral, or badly. So let it go :) Until the next time you stand up for the rest of us :)
You sir are a hero :)