I cannot redeem my gift card

There's several kinds of gift card fraud. Here's what Apple says if you cannot redeem a card:

If you can't redeem your App Store & iTunes Gift Card, Apple Music Gift Card, or content code -

https://support.apple.com/HT201195#inactive

Unfortunately you kind of get caught in the middle as each company tells you to go to the other. :-(

You can also report fraud to the police and see if they will discuss the problem with the card company and vendors involved.

In future try to redeem cards the instant you have purchased it. I usually do it in the store immediately after having paid for the card should I need to approach the store's customer service about a problem.

Hello hong,

See if information in this document helps: If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - http://support.apple.com/HT201195