i need to change my apple tv billing to my new country

i was in australia when I set up my apple tv, i am now in nz and need a new credit card to pay but i can't seem to change my country in apple tv billing. I've changed it on apple ID, restarted and ....apple tv says the nz card number isn't australian so enter an aussie number. but i'm in nz and all aussie cards are history. round and round.