Has it been confirmed it’s unroadworthy? 11 Plate, I assume it’s got a pretty recent MOT cert then?
The problem I see is that very many cars get crashed every year and repaired – if it’s not a ‘write off’ it’s not even recorded – repaired doesn’t mean returned to factory fresh condition either – things can be out of perfect alignment, in fact no car is 100% straight, if they were, we wouldn’t need to have the wheels aligned from time-to-time – even Ferrari will consider a repair to be ‘factory correct’ if it’s less than a certain 100% out – it might be as high as 5%.
Unless the OP can get someone of ‘standing’ – I.E. an MOT tester, or AA inspector etc to say it is unroadworthy then I don’t see the garage being liable – they’ve made clear thought one of those horrible statements they make that the mileage is wrong unless otherwise stated – if it’s not been ‘written off’ and had a CAT C or D recorded against it which they didn’t declare then they haven’t done anything wrong (moral issues aside).