How to request a refund to my debit card?

Hopefully you do know where this charge came from, otherwise it looks like your Apple Account has been compromised or your Debit Card has been compromised. If it is your Debit card that was compromised, then contact your bank, and if your Apple ID was compromised then review this support article:

If you think your Apple ID has been compromised - Apple Support

There are situations where you are responsible for charges on your account:

• If you are a Family Organizer and use Purchase Sharing, then other Family members are allowed to purchase items on your payment method.
• If you give someone your Passcode, then you have authorized them to use your device and that includes making purchases.

This is primarily a user-to-user support forum; other Apple users like you. We don't have access to information about charges to your account. Apple has a support article about charges — see each of the steps in the following instructions. They include information on contacting Apple Support if the other steps don't help. See: If you see 'apple.com/bill' on your billing statement - Apple Support

If it is a recurring charge, also see: If you want to cancel a subscription from Apple - Apple Support

There is an Apple article with information about requesting refunds. Click on the following link: Request a refund for apps or content that you bought from Apple - Apple Support