Interior fire at Dacia Logan MPV 1.4 built in 2009

I have a problem! My cousin’s car (Dacia Logan MPV 1.4 petrol, built in 2009) burned down last week in the interior, rear seat area and rear passenger door. It was cleared by the fire department. Now I come to my problem. Renault/Dacia is a cable fire in this vehicle not known and refuses to deal with the damage. My cousin is a non-smoker so the fire cannot have been caused by a cigarette and the vehicle was concealed Since the vehicle is only subject to liability, the insurance does not cover the damage that has been caused. Is anyone familiar with this or who has already done it? I would be very grateful about your help and I am glad about every answer. With kind regards Schnubbel1