I had an accident with a car I rented from a person who turned out to be unauthorised. What to do?

I rented a car from a person and in our conversation on WhatsApp, I asked if he works for the shop and he confirmed he is the owner.

I rented that car. One person came and handed the car over to me. I signed only on the checklist for car inspection then I had an accident in the car.

I called the police and made a police report then I discovered that he is not working for that company and he is not the owner of the car I took.

He wants me to pay 25% + stoppage days for the car rental. I tried to reach the company that owns the car and they told me over the phone that the car was out without agreement.

What should I do now and to whom I should pay the claim?

I don't know the owner car company and what is their policy.