.I used the garage I have used for years....ex Scoda dealers.
UPDATE
Driving along this afternoon and she started vibrating, only 6 miles.
Definitely not taking her back to this garage
The least you need to do is to send a strongly worded letter to the Service Manager, telling him if your findings and that they are lucky they aren't being taken to court for criminal negligence!
It might be worth sending a copy to Trading Standards too.