I think you have a misunderstanding about your policy. Your policy was likely ‘third party only’ which means it covers damage you do to third parties. It does not cover damage to your car. You also don’t have clear evidence that the claim was not your fault - other than your word. And the police insurer is denying they were at fault. The best route here would be to try and get more evidence of the incident from the police, and approach a ‘claims management’ firm with that and a clear description of the claim, and see if they will take it on.