My dad had a similar situation happen where a detailing company damaged his SUV and refused to pay or fix it because their sign said "we are not liable for any damages"
He took them to court and the judge said to the company owner "You don't have a leg to stand on because there is no legal contract".
The person or company that takes your vehicle into posession is 100% liable for anything that happens to it unless you sign something otherwise, but that would just be stupid.
Needless to say my dad got every penny for damages and the owner had to pay for all the court fees.
I'd like to say good luck, but you won't need it. You'll everything you want from them in the end.