Claim rejection

I had a comprehensive cover. My engine over heated. I took the car to the garage. The insurance said they ar not going to fix my car because what happened to the engine was negligence. How?, i don't know. When i requested telephonic conversation records to prove that when i took this cover they said it includes mechanical damage, they simply stopped replying to my emails. When i call I'm always told the person who can a answer is not at worl. It's been 3 weeks. I am fixing my car on my own. Do not make the mistake i made. Switch insurance while you still can if you are with them already. For those who want a new insurance, i would edge you to consider others than them