Hi Mike.
If it’s a genuine human error, they are allowed to fix it and offer you the car at the correct price. However, you have the right to refuse to proceed with the new price and get your deposit back.
It’s poor form not to call you up when it was first discovered (probably months ago) to inform you. Simply presenting you with an invoice for a different price is unacceptable behaviour.
Personally, I’d be making a complaint to the dealer principal. If he/she still refuses to honour the original contract, I’d walk away and find a different car.
The dealership is probably hoping that you won’t cancel, especially since you’ve been waiting five months for this vehicle, and therefore you’ll simply accept the increased price.