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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

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.

Get in touch with your bank. They will reverse it