Koons Tysons Toyota (Service Dept.) Damaged the rear bumper by one of their employees Vienna Virginia

I dropped my 6 month old Toyota RAV4 at the Koons Tysons Toyota service center to have them check for a leaking tire. My wife and I had both inspected the rear wheels for low pressure in the morning, and during this inspection we did not find any dent/damages to the rear bumper. So I drop it off and 1 hr later have my car back. I drove it about 10 minutes to a store nearby. I parked the car in front of the store window (a huge glass window) and walk in. I remember that I have left something in the back seat of the car so I go to the car and there it is - a big dent on the bumper; A BIG NOTICABLE DENT! I then go back to the service center and talk to Aria Moshefri, the technician that usually helps me with service/oil change. I start telling him about the dent and even before I complete my sentence he goes "oh! the dent on the back, yes, we know about it"!!!!!!!!!!! HOW IN THE WORLD DOES A GUY THAT SITS IN FRONT OF THE COMPUTER TO ENTER DATA KNOW ANYTHING ABOUT A DENT IN THE CAR HE HAS NEVER SEEN??? So he comes out to the car and tries to prove that it is an old dent by telling me there is old dirt covering the dented region. It doesn't make sense to me because if the dust/dirt has settled hard on the metal no matter how hard you hit, its not going to just fall off and become clean because of the impact, and please correct me if I am wrong! So I immediately take it to a nearby body shop that I trust. The guy there tells me the dent is brand new because the paint particles coming off. So I go back to Koons and talk to Aria's manager Chuck. This gentleman, until now who knew nothing about the damage, starts to defend his workers even without questioning them! How in the world does he know what happened behind in the shop when he's himself sitting in an AC room right next to where Aria sits? He blatantly denies that his workers had anything to do with the damage without doing his due diligence.

I called my insurer, Geico, and they tell me if Chuck et. al. denies having caused the dent then there is nothing they can do about it and that I will have to fall back on the uninsured motorist part of my coverage, the deductible for which is $200.

I just don't get why I have to shell out the $200 when the dent happened when the vehicle was under Koons Toyota's supervision. I really don't know what I should do or how to get them to accept their mistake. Any/all help/advice appreciated!

Dissapointed_with_koos_toyota
Vienna, Virginia
U.S.A.