Enterprise Rent-a-Car Charging me 600$ for a 1 inch scratch I didn't cause!! Hamilton, Ontario

I have rented cars from Enterprise few time before and I did not have any problems with them and so I didn't suspect that they would fraud me this way. When I picked up the car, we did a really quick walk around and I trusted the representative. However, I did notice he was extremely quick with the walk around. over the 4 day rental period, I can assure you that there was nothing that could have caused any damages because the car was parked at the hotel for the entire time as we used public transportation and walked around in montreal downtown. When we returned the car, they found a "1 inch scratch on the front bumper" which may have been there when I rented the car. it was so small that there is a high possibility of missing it when he did the walk around. It would have been impossible to notice the scratch in the walk around as it was so tiny and it was right at the front bumper in the middle and the car was facing the rental office that we did not even take a look at the bumper! He quickly filed a report, and the representative was very rude! he did not explain that it would be sent to a collision center or anything, he has told me to pay a 100$ for the damage and that it would be sorted out! he DID NOT indicate that the 100$ was only a deductible! He did not mention anything else. Couple weeks later I received a letter from the damage recovery unit stating that the damages cost close to 600$ and have contacted my insurance company without my consent and now it is on my file affecting my insurance! 

what I don't understand is that how can a 1 inch scratch cost me 600$ that I did not cause. I can guarantee that I did not hit anything and had no damages while the car was in my possession. I feel truly scammed as a student, I cannot afford to pay this damages! 

Enterprise Rent-A-Car are rude and they rip you off!