I would get it back from the bike shop and tell them that you will spread the word that they are a bunch of cowboys. Then get it repaired somewhere else.
The lesson here is Buyer Beware.
Badmouthing someone without understanding the exact circumstances is cowboy behaviour in itself.
Surely the lesson here is: Buyer, go educate yourself about things mechanical? Speak to the mechanic, try and understand what went wrong and how to prevent it. Believe you me, he doesn't like incidents like this and would rather spend a few minutes with someone explaining, than have to deal with threats and storms in a teacup.
I am always willing to rubbish bad customer service.
Steve, you've made up your mind about this, haven't you?
I've seen so much of this in my time working on bikes. I've been accused of rusting a bike headset within the 24 hours that the bike was in our shop, I've been accused of ruining a hub's bearings, races, cassette and looks just by opening it in front of the customer and also of supplying very weak rear derailers that jump into the spokes all by themselves each time Godzilla the owner makes a monster forced shift.
Each time with each the these cases there were three common denominators: 1) I was apparently at fault - even by remote and proxy 2) The owner had not a degree of mechanical sympathy at all. 3) The owner threatened to make a scene and go to social media and tell his friends and shout his head off in the shop.
In about 20 such cases over seven years, only one man ever looked me in the eye and said sorry, he now sees that he is at fault. He's the one who ate rear deraillers for breakfast. I cured his problem by taking him out for a ride and teaching him how to shift gears. I wish I could do it for every customer but there's not enough time in the day to do that.
I also wish my skin was thicker so that when confronted by people like you, I could just shrug it off and smile. But, I couldn't.