Not nearly enough precise detail on the cost of the labour and the quality of the parts fitted to form an informed opinion however IMHO you have been well shafted and to be brutally honest you only have your self to blame. Wake up and smell the coffee.
I really do hope that you learn from this, however, never the less it is a very expensive lesson to be learned.
As has been said, take some one with you when you go to collect
Also I think that you should definitely name the garage.
When I read through this post I was of the opinion that this must be a wind up as nobody can be so naive or gullible.