I'm afraid I'm with Ekona on this one. I don't doubt what happened at all but you would have to be able to prove that 1) it was definitely the cause of the accident and 2) that it was they who put the wheels round the wrong way. Short of a confession there are just too many ways out for the garage and to try and pursue the legal route may end up being stressful, frustrating and expensive. I really feel for you but I think you may just have to take the hit (excuse the pun).
Good luck.
+1 I'm afraid,
Never ever nice when this sort of thing happens and whilst these days there is an increasing tendency to look to others for blame/compensation I presume you chose not to take out track insurance which is the option that would helped you, after the excess, to recover much of the expense of putting your car right.