you're f**ked now.. should never have told them it had minor dents and scratches.. that is to be expected with any older car, and cannot be expected to be in 'as new' condition 15 years later.. barring major dents or obvious roadworthy items.
you could argue that in court with any compentant lawyer, and they should be able to slaughter the insurance company, even with their lawyers. Its just a fact of old cars, they are no longer 'perfect' (within obvious limits of course)
I suggest getting the dent doctor out, popping out the minor ones.. getting a receipt for the fix, and shoving it in their noses.. as 'fixed'. Take photos if required.