I can't activate my iTunes gift card

This is a user forum. You are not talking to Apple.

Contact Apple support.

Where did you get the gift card? The retailer may not have activated it properly at the point of sale.

If you did not purchase it at a retail store or directly from Apple, it's likely it was stolen and never actually activated.

You may want to go back to wherever you got it.

See -> If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card

If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support

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Contact Apple Support -> Contact Apple Support.

You might need to provide:

• An image of the full front and back of your card.
• A sales receipt showing when your card was purchased.
• The serial number from your card. 

Beware of -> About Gift Card Scams -> About Gift Card Scams - Official Apple Support