I should talk to local consumer bureau in respect of a claim under s75 of the Consumer Credit Act.
https://www.financial-ombudsman.org....-bought-credit

This should be 'fit for purpose' and applies even if an item is out of warranty period (or none at all), especially when paying a five figure sum..
Did you pay ANY of the cost using your credit card? If so then again under s75 your card company is jointly liable for a claim along with the garage.your