Sixt review: Rental car overcharge

I rented a car in Los Angeles, returned it after one day as I no longer needed it. signed out with checkout person. Went to hertz to pick up a different car. I never relied receipt until 3 days later. Receipt claimed I returned car on 7/20 at 904pm. they produced a fraudulent electronic signature receipt. I flew out at 6am that am, so I physically could not have signed at that time. Furthermore their receipt had contradictory information. Claiming I returned the car they day before(still not accurate). however they have no signed electronic receipt for that drop-off. I was in a different part of LA at the time I can document that I couldn't have returned car then either. furthermore they sent a damage claim on car, which didn't exist when I had car, and the photo of the hand of the person in photo was a female and not the person I returned car to. They subsequently refused to return my charge, and took my security to boot. I sent my flight information, garage from hotel info, and other supporting docs but to no avail. Im writing here before I contact my lawyers. Sixt has committed billing, Maile Fraud and stealing my security deposit. They have told me I can no longer rent with them and they will try to impact my credit.