You ask for their companies insurance company, they had control over your vehicle by an act "of Bailment". Did they check your vehicle over prior to driving off? Do you have any photographs of your vehicle prior to letting them take it? Always photograph your vehicle prior to leaving it with someone, in the same way you should photograph any hire car before receiving it. Ultimately it could end up your word against theirs. Do they have CCTV? Can you prove the condition prior to leaving? You need to substantiate your viewpoint.