How can I change Country/Region when I still have store credit balance?

I registed an iTunes account when I lived in Japan and I used Prepaid Card to redeem Japanese Yen to account (Country/Region=Japan). I have 60Yen in account now, this amount is smaller than cheepest apps (cost 85Yen).

Right now, I came back to Vietnam and want to change Country/Region and to continue purchase apps in Apple Store:

- When I change Country/Region, I received error message "You have a store credit balance; you must spend your balance before you can change stores.". But I couldn't spend money due to not enough money.

- When I change Payment Type to Visa card, I received error message "You payment method is not valid in this Store. Please enter a new payment method."

How can I change Country/Region when I still have store credit balance? Please help me solve this issue.