Hi Folks

Someone hit the rear of my A3 Sportback 2.0TDI (2004) 140bhp
Just above my exhaust, centimeters away.

Sine the accident my engine management light has come on.
Took it to the repair centre who advised its problem with my egr valve or its sensors.

This only occured since the other vehicle hit me in the rear.

Third party admitted liability for the repairs to the body but will not repair my egr valve problems.
They are saying that Engine Management Light has nothing to do with rear impact but EGR is connected to the exhuast where the impact occured.

How do I prove that impact to the rear of my vehicle done this please?