Absolutely right, what a bloody cheek the dealerships has. Doubling the delivery time is clearly unreasonable and due cause for cancelling and refusing a deposit back is a joke.
Cancel the order, buy a second hand one tomorrow and take the dealership to the small claims court for being *ankwers. As stated above they would have no trouble selling "your" car even if had been started to be built at the factory.
I have no sympethy for dealers who behave like this and Fiat should jump up and down on thier heads.
Fiat CS should also be ashamed of themselves too. They seem to have washed thier hands of you with the statement that its between you and the dealer.