I received an email about the refund but my account has not been refunded yet

After you request a refund you'll receive a status update by email within 48 hours -- which it sounds like you have indeed received with refund approval. The money is returned to the payment method you used. The time it takes for the money to appear on your account or statement depends on the payment method:

- Store credit (e.g., Apple ID balance): up to 48 hours

- Mobile phone billing (payment through your phone service carrier): Up to 60 days

- Other payment methods (e.g., credit/debit card): Up to 30 days for it to appear on a statement.

For apps and media you can also sign into https://reportaproblem.apple.com to check if the status of your item is "Refunded".

From: 'Check the status of a refund for apps or content that you bought from Apple' --> https://support.apple.com/HT210904

If you need to contact Apple about this, click on this link --> https://support.apple.com/choose-country-region/ and choose a path that gets assistance from Apple staff.

Refund for what? This is not Apple support, this is a peer to peer user support community. Please do not post sensitive information, such as your Apple ID, or credit/debit card details, here. How did you request this refund? For refunds for App Store purchases, you need to follow the instructions here: https://support.apple.com/en-gb/HT204084 (please be aware that not all purchases are eligible for refunds).

Finally, you may find it easier in future to post to the Vietnamese language forum. https://discussions.apple.com/choose-country-region