Theft of insured clients

I drive a Nissan 370Z and need a windscreen replaced. I completed my claim form but there are no windscreens in the country for the PG Glass does not have one. I approached Nissan Melrose to import me one seeing that there is no windscreen in the country. I received my approval ref number from the glass company for fitment and eventually after two weeks of battling got a date for fitment. I got a call this morning to tell me that I must pay a 25% markup on the windscreen to the glass company even though they did not source or buy it out, for Nissan still has it with them and the insurer pays Nissan directly. I even pay a 25% mark up or their fitment pricing. I think this is absolutely theft to the public and it does not mean that because I am insured that either the insurer or client must be **********. I should only pay for the fitment and the normal access of the cost of the windscreen as invoiced to me by Nissan not after PG Glass just adds their 25% without sourcing or buying the windscreen. I do want to warn all people using PG Glass to be very careful and have a good look at your invoice and what you are being charged and are paying for. This is wrong and incorrect.