Damaged courtesy vehicle

My insurance referred me to Europecar for a courtesy vehicle while repairing my car. Unfortunately i did not received the vehicle that was booked for me. In a rush they gave me another vehicle for which i was very grateful just to find that the car was very dirty on the inside. Looked like someone messed something on the back seat and someone smoked in the car, so the smell is unbearable. When i got home i put the car in the garage overnight. Next morning when i removed car from the garage i found so much oil spillaged on the floor, i was very concerned and informed them about the situation. We phoned them and they said they would bring me a new car to go to work on monday but after a few hours of no show we phoned them to hear when they will come, we suddenly had to pay for the damage on the car. They(3 different consultants) said we should drive the car back to Europecar to change the car, but if the engine gets damaged who will have to be responsibility for this? Why do i have to pay for the damage if i didn't do the damage to the car?