National Car Rental Scam trying to bill me for damage to rental car I did not cause!! Extortionists! Houston, Texas

I rented a car from the Houston Hobby airport location; upon receiving the car I noticed several large scratches on the car. I thought that it was odd that a car in this scratched condition would be rented so I took several photos on my mobile phone (quality of pictures are poor since the glaring Texas sun did not allow for proper photos). Since I felt confident that they were knowingly renting this car in this condition I did not say anything to the gate operator who opened the gate for me to exit. Upon returning the car, the staff at National Car Rental asked if knew that there was a large scratch on the car. I told him yes and that I had photos. I showed them to him and he said he couldn't make them out and then proceeded to tell me that if the scratches did not show up in his computer system then I had to of caused them, thus accusing me of causing the scratches. I told him if he and his team did not perform the ACTUAL due diligence necessary on the vehicle prior to me renting this vehicle then it wasn't my fault that they were not properly maintaining their computer systems. No one from National offered to do a pre-inspection of the car and since I am an Emerald Club member I merely got into a car that was waiting for me.

 In essence he called me a liar and informed me again that his faulty record keeping system did not reflect this. How in the world if no prior vehicle inspection was performed with me can they accuse me of causing this damage? This is just a devious attempt for me to be extorted to pay for damage that someone else had caused and since the current management team and process are inadequate, dishonest, corrupt, and a crooked business entity I am expected to pay for a poorly run and poorly managed organization. I received an invoice from a Recovery Specialist stating that I now owe them $505.60 for these damages. They have my credit card on file and I am afraid that they will exercise and demand payment of damages that I DID NOT cause...PLEASE HELP PROTECT ME AND THE PUBLIC FROM THESE CROOKS!!