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To "Request a refund for apps or content that you bought from Apple" click on this link --> https://support.apple.com/HT204084

Get in touch with your bank. They will reverse it

If it was a mistake on Apple's part and this is registered as a fair charge by Apple, putting a block on the payment through a bank may just result in Apple putting a block on the account until it is resolved. It is best to work through Apple's system unless the user is certain the charge has nothing to do with Apple.