I’m going to try and be constructive (I know, I know).
The OP’s complaint is definitely legit, the bike shouldn’t have left the shop like that, lack of response from shop/head office is also poor, you’re right to feel aggrieved about that.
If you want to take something positive out of the situation (other than not getting deaded) I think there’s a couple of points to be taken away.
Firstly, escalate the complaint as soon as you went back to the shop, ask to speak to the manager there and then, make them aware of the situation and ask them what well be done, not in a “fire him now” way but a “how did this happen? What will be done to stop it happening again” way.
Secondly, use this as the spring board to start picking up a bit of knowledge regarding maintaining your own bike. There’s no piece of mind like that of doing the job yourself and knowing everything is in order.