1,500yen worth newly redeemed itunes gift card: gone!

i bought and redeemed a 1,500yen worth of itunes gift card and still haven't bought anything in the App store. I redeemed that for me to be able to change back to Japanese store. but when I was going to buy an app this day, I saw that there's no balance. how come? where did it go? isn't it unfair that I just wasted 1,500yen for nothing but just changing of stores?