Insurance refuses to pay out for damaged mag

Had an vehicle accident in Oct 2014.I was asked to send quotes for repairs to be done. The damages to the vehicle was fixed (bumper and rim and rear ex-haul), but my insurer refuses to replace damages to my mag wheel where the impact took place. I have my mag wheels covered as specified. I was advised they are unable to source the center cap of the mag wheel and therefor refuses to replace this. I always ensure that my policy is up to date,but its as if my insurance all the reason possible not to pay and put my asset back to its status before the accident.