ITUNES

Have you looked at your purchase history ( See your purchase history in the iTunes Store on a Mac or PC - Apple Support ) ? If you can't see where it went have you tried logging out and back in ? If the balance doesn't change you could try contacting iTunes Support and see if they can help : http://www.apple.com/support/itunes/ww

Did you owe iTunes any money ? Have you checked the account's purchase history ? Have you tried logging out and back into the account and seeing if your balance changes ?