Thats not good.
You could try trading standards for advice, but i don't think you are going to get anywhere.
Problem is you will need to get the car independently inspected to see if you have a case that they have bodged it.
By time you have paid for that you might as well paid someone to do the job.
I would post on the 'good guys section' , tell your story and tell everyone on here to stay away from them.
Do the same on clubgti as well.