Have you can contact Apple Support to request a refund? , see -> Check your Apple Account balance
Check your Apple Account balance – Apple Support (UK)
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If you have an Apple Account balance that you can’t use
You can't redeem or return Apple Gift Cards, App Store & iTunes Gift Cards or unused Apple ID balance for cash, except as required by law. If your jurisdiction allows the refund of redeemed gift balances, you can contact Apple Support to request a refund.
When you contact Apple, include the following information:
• Your Apple ID.
• The refund amount.
• Your current delivery address.
How long that it take we don't know, we are also users of Apple products & services like you.
At least It would take about 1 to 3 business days in order to process.
Contact Apple directly -> Get Support or call Apple in your region see -> Contact Apple for support and service or check -> here for more support and assistance.