@Charlotte570 This shouldn't be possible. The host's advertisement may have very well been in US dollars, but that amount would have been shown to you converted to NZ dollars. Guests are shown pricing in their own currency. I list in Canadian dollars- but if a Mexican guest is looking at my listing, they will see the price in it's Mexican peso equivalent, a US guest will see it in American dollars.
I suggest you contact Airbnb to work this out- they are responsible for the platform and how the prices are shown and they are the ones who deal with guest payments.. And the host may be confused- the host may think that what you have paid (half up front) is the full amount that is being charged.