REJECTION OF MY MY BURNT CAR CLAIM

On the 10th of April 2015, my car burnt between Komga and Bisho but the fire did not affect the body of the car, the fire was underneath the car and there was huge smoke coming from underneath my car, I stopped the vehicles that were passing by for assistance, I got help from a truck driver who driving a Truck of Spar, he took out a fire extinguisher which saved my car from burning beyond recognition but the engen exploded while the guy spraying the fire extinguisher. Now my AIG insurance which I took through strata insurance brokers is rejecting the claim saying its a mechanical problem or the car was overridden which resulted to the damaged and they oppose that there was fire and they can not take responsibility to pay such claim. I am seeking for assistance to get my car repaired or get a new car because now my insurance running away from taking the responsibility. I even spoke to AIG claims manager (wessel) who confirmed the rejection of the claim.