In our experience typically in the situation you described the owner of the car that hit the parked car would be liable. If the owner's insurance is denying a claim you should request more information on the reason. There may be other circumstances involved. If you cannot resolve this issue with their insurance company and you believe they are being unfair, check with your state's insurance regulatory body to see what your consumer rights are.

Beyond that, if you have collision coverage you could make a claim with your insurance company for the damage. You will have to pay your deductible but will be able to get your vehicle repaired.