I want a refund for my purchase

You do not say where you see this purchase. If it is an e-mail or text message are you sure it is real and not an attempt to steal your private information ('phishing') (very common)?

Phishing & Other Suspicious Emails - Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

Identifying legitimate emails from the iTunes Store - Identify legitimate emails from the App Store or iTunes Store - Apple Support (the previous link is more specific)

Forward attempts to: reportphishing@apple.com

If you still think the charge is real:

See your purchase history in the App Store or iTunes Store [iOS, computer, or web] - Does not list purchases made by others under Family Sharing; those have to be checked from their accounts. View your purchase history for the App Store, iTunes Store, and other Apple media services - Apple Support

Also follow the steps in this support document --> If you see ‘itunes.com/bill‘ or an unfamiliar charge on your bank, credit card, or debit statement - If you see 'apple.com/bill' on your billing statement - Apple Support

If neither you nor a family member (if applicable) has a record of this purchase and you only saw it on a statement for a card you alone control, contact your bank or card company about card fraud. Apple does not handle that.

If you do now recognize this purchase and are asking for a refund then realize Apple's terms of purchase for most countries are effectively, "All Transactions are final" (check terms at: Legal - Apple Media Services - Apple ). Apple does refund on a case by case basis, but they can also refuse.

To "Request a refund for apps or content that you bought from Apple", click here → Request a refund for apps or content that you bought from Apple - Apple Support

Report a Problem - https://reportaproblem.apple.com/?s=6

If a reporting a problem request is unsuccessful you can also try clicking here → Choose your country or region - Official Apple Support Select your country, then a product.

What did you purchase and from whom did you purchase it? We need more information if we are to help.