Claim Rejected without a valid reason

In August 2018 my car was involved in an accident, I submitted a claim with Auto and general and the claim was approved, and the car got repaired. In December 2018 Auto and general contacted me and sold me Pre-owned Mechanical Breakdown Warranty policy. On the 05 August I had a car breakdown, I got the car towed to Bosch Hillfox for inspection and they have found the issue. The problem was caused by the alternator failure which affected the ecu and battery.

I submitted a Mechanical Breakdown claim with Auto and general they rejected my claim saying that they won’t pay as my car was once involved in an accident. Their policy says it does not cover “damage caused by theft, hi-jacking, an accident, misuse or neglect” and the failure on my car was caused by none of the mentioned exclusions.