Why I buy itunes then no balance

The gift card you’re trying to use has already been used.

If you did not use it, go back to the retailer where you purchased it.

Well, you have asked us to guess everything about your particular situation.

Maybe you spent all the funds in your Apple account. Perhaps you never had any funds in your Apple account. Maybe you have an Apple Gift Card you failed to redeem. Maybe …

Then talk to whoever you bought it from. It’s worthless. It’s already been redeemed buy someone.