Burnt VW polo vivo

Good morning I need some advice with my 2017 polo vivo that has been burnt. The insurance company (Discovery) has disputed the claim saying that it was a mechanical failure and that they do not cover wear and tear parts, also they had a fire investigator that was not registered with the South African fire council, I took the matter up further with VWSA and they did their investigations but could not find the cause of the fire and when I questioned them what caused the fire due to the vehicle being just 2 years old, they ask me for components such as the bumper and illumination lights that were burnt in the fire, tried taking the matter up with the ombudsman of motor industry but they want me to get a forensic fire expert to investigate the cause of the fire and then they can make a decision, if anyone has any advice please help.