They can't possibly do that. The burden of proof is on them to prove that you gave them the wrong model number. If they can't prove it they have no leg to stand on. They're trying to use it as a get-out clause, well they can't without proof.
Bit worried now as I've just taken out the house insurance with kwik-fit. I might give them a call and say how they've treated you is making me want to back out of my policy.