damaged with wrong screw during tyre change wheel bearing

Hello together this is my first post here. Last November I had a car dealer with whom I have been a customer for many years and already the third car drive my tires on winter tires changed. This is now the third change. This was always done in this workshop. My wheels are also stored there. Last week I wanted to have changed from winter tires to summer tires again. I was told that there was a problem with the wheel bearing and that they had a I could not change the tires. I should drive to Smart with them. I did that too and described my problem. There you could not imagine how such damage could occur. This morning I brought my car there for cost estimate. Before that I got the call back.The employee of Smart. informed me that either a screw was screwed in wrongly or one with broken thread, so that the wheel bearing was destroyed. As I said, it has never screwed anyone other than this Wekstatt there. The damage is 600Euro. Is there a mediation point of the inside or similar? That only if the dealer does not show himself. Thanks already once for your answers