refuses to repair my Vehicle's gearbox.

I had a small accident with my Mercedes. The rear of my car was damaged and the gearbox got damaged(The car can chance gears between Park , reverse and drive. But once it is in drive it only remains in 1ste gear)<br> The claim was approved, but on the claim it was stated the gear box was subject to inspection.<br> <br> Mercedes sent through a report that the damage was not accident related. Thus Discovery now refuses to repair the gear box. After several phone calls Discovery refuses to see my point. The car was in a 100% perfect condition, but after the accident the gearbox was not working as it should. How can this not be accident related?<br> <br>