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If Apple has approved your request, see this Apple article: Check the status of a refund for apps or content that you bought from Apple

Check the status of a refund for apps or content that you've bought from Apple – Apple Support (UK)

When will I get the money back?                                            

If your refund is approved, the funds will be applied to the same payment method that you used to buy the item. 

Here's how long it takes for a refund to appear on your account or statement:

Store credit – It may take up to 48 hours to see the refund in your Apple Account balance.

Mobile phone billing – It may take up to 60 days for the statement to show the refund. Processing time may be affected by your network provider. You can contact your network provider for an update.

All other payment methods – It may take up to 30 days for the statement to show the refund. If you can't see the refund after 30 days, contact your financial institution.