False damage claim

I only had the car for 5 hours from LAX to San Diego and turned in the car with no issues. Then after a few days I get an email showing damage to the from bumper that conveniently left out the front license plate. They are coming after me for $1,259.59. They will not answer their phones during the normal business day instead sending me to VM to call back during "normal business hours". The photos they sent are no longer available in their portal for me to see them again. I asked them to send me via email timestamped photos with the license plate and the previous intake report, but I get nothing but radio silence. Other members of my family have had similar experiences with Sixt. Beware and avoid them at all costs!