Car burnt 3 days after service

On 22 Jan 2015 my Mercedes Benz C180 was serviced at Mercedes Benz Centurion.On the 25 Jan ( 3rd day after the service),the car was driven to Randfontein and parked in the Fruit and Vege yard.2 minutes after parking, engine started burning and was extinguish. It didn't give any notice of a problem.Mercedes-Benz analysed the cause and concluded:<br> There is no observable evidence that an inherent or latent, product-related fault on the vehicle existed or was a possible cause of the fire furthermore mechanical or electrical failure may be in all probability reasonably excluded. <br> There is also no evidence to indicate neglect or an incorrect service procedure by the dealership during the recent routine service<br> The cause of the fire may in all probability, be attributed to the ignition of dry grass or similar vegetation from beneath the vehicle as a result of contact against the CAT or exhaust tube<br> I don't understand the grass issues because the car was in a tarred parking. I will be very scared to drive the same car again after repairs what if it starts burning again because MERCEDES BENZ FAILED TO IDENTIFY THE CAUSE OF FIRE AND TAKE RESPONSIBILITY.I have lost confidence in MB cars