Enterprise Rent a Car Vallejo, California Enterprise charges for pre-existing damage Vallejo ,rental office, California

We were framed for pre existing damage on a rental car from Enterprise. 

We rented a 2013 Yaris from the Enterprise in Vallejo in October 2013.  We had an appointment for 9 but the car did not arrive on the lot until 9:30 The people who drove it in said they had just been getting the car detailed. The agent conducted a hasty inspection asking us to  look for evidence of         " scratches, dings or dents".   My husband noticed little chips of paint scuffed off the edge of the front bumper but the agent said that it was nothing and we wouldn't be charged for it . The seats were wet when we got in but we were already late.  

We returned the car four days later.  

On that inspection however, the agent pointed that  2" piece of plastic  missing from the decorative grill.    We said we didn't know anything about it.  Then she walked to the driver's side.  She took one finger and pried  the edge of the fender panel out.  This she said, was  an indication of  a front end collision.  We said it seemed just to be unclipped but she said NOW she would have to fill out a damage report. 

We were stunned.  We said we were unaware of any damage to  the car while we had it.  

While she was inside on the phone we noticed that the passenger side fender was unclipped in the same way . Whe we showed it to her, she said  that it was  just a further indication  of a front end collison.  

It was surreal.  My husband again pointed out the scuff marks under the front bumper that he had mentioned  in the pre-inspection, she told us,  without looking at the bumper, that it was not related.

The agent  found no scratches on the car and  admitted that she could find no damage on the surface of the fender, nor the hood or the bumper itself. Other than the 2" piece of decorative plastic there was no indication that anything was amiss with the car.  

We asked that she contact the agent who had done the hurried pre inspection but she said that the agent worked out of another office and could not be contacted.  She demanded we give her our credit card and insurance information.  She was bellligerent and we declined .  She did not return our copy of the rental agreement .  

Two weeks later, we received a letter,  asking for our credit card insurance information so a claim could be processed.  We called back immediately and explained that we were not responsible for the damage.   Two weeks  later, enterprise called and said  the regional office  had investigated the damage report and decided we were responsible and owed them $698. We still have not received any paper work explaining or substantiating the charge  or the damages,  including  photos, inspection reports or mechanic's invoice.