Try a few other dealerships and don’t mention any fee for metallic paint
I had a similar issue when I ordered my car in Oryx White
the first dealerships said – Nope you have to pay the full £1035 , Motability twice said – Sorry you have to pay the full price and not the difference between Free Metallic and The Oryx White
but then I spoke to a couple of different dealerships including the one I ordered from and they were More Knowledgable & Nicer People who were more than happy for me just to pay the difference between Free Metallic ( Value ) and the Oryx White
so sometimes it’s how you say something and approach it you know?
Good luck