Claim not handled well and affecting the outcome

I am extremely shocked by the way my case is handled. My claim is apparently declined (haven't received official communication in writing) because there is "no enough proof" that I did not give consent to a drunk person to take my car and crush it. I have provided all the information that I could possibly could to prove that I did not give the person my car, but their investigator still expects me to provide proof... When I ask what the proof could be, he also doesn't know what proof could be used. 1st, they only started investigating my claim after 3 weeks of the claim. When I ask the investigator about the information he was able to get, his updates are never the same, the story always changes to suit them - even when I pose logic questions to him to show that his story doesn't make sense. He is using the perpetrator's friends statements to make his conclusion - they are friends obviously they will support their friends. I am sure they were not questioned for details to see if their story is adds up, it's the same as saying that your car was ****** and you are asked to provide evidence that you didn't give it away because it was ****** by someone you have met before. Had the investigation take place earlier, camera surveillance could have been obtained, and I am not left to fend for myself because they don't want to pay. I can't even get a straight answer from the argumentative investigator on why my claim is declined. Can I please be contacted by a superior to look into this claim again - not by someone who is possibly trying to secure their YEAR END BONUS by rejecting claims.