A REASON TO REJECT A CLAIM

My son was in a terrible car accident on 10 March 2017. He's best friend died and my son obtained a neck fracture and head trauma (bleeding on the brain) and suffers from retrograde amnesia. Claim was lodged. After much deliberation i was informed that claim was rejected due to unroadworthy vehicle. Cannot understand this as vehcile was regularly serviced and maintained. Reason given was that one tyre was re-grooved. I have no knowledge of a re-grooved tyre and travelled many kilometres on that tyre. In fact i was told that the tyre caused the accident. Vehicle was taken to anther city and too date i have no idea what to do as M&F is saying its my responsibility to get the vehicle back to my place on my expenses.