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Your account in your new country should use a credit card supported by a bank in that country. Your residential address must be the billing address in that same country.
As far as change goes. You cannot change countries if you still owe money in the previous country. (Of course, I don't know that you do.).
You need to have a card issued in the country of the store in the region you live. Since you are in Austria, you'd need a card issued in Austria. I'm guessing you don't have a card issued in Austria? You could get around that by using iTunes gift cards if you can't get a card from the country of residence.
Question: Why can't I change my country?