I was charged twice for a purchase that I made

Click on this link and read it to "See your purchase history in the App Store or iTunes Store [iOS, computer, or web]" - If you are a Family Sharing organizer you will not see items purchased by others but which may appear on a credit card you own; those have to be checked from their accounts.

http://support.apple.com/HT204088

Read all the steps in this link -->

If you see ‘itunes.com/bill‘ or an unfamiliar charge on your bank, credit card, or debit statement - https://support.apple.com/HT201382

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 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: https://www.apple.com/legal/internet-services/itunes/us/terms.html ). Apple does refund on a case by case basis, but they can also refuse.

Request a refund for apps or content that you bought from Apple - https://support.apple.com/HT204084

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

If a reporting a problem request is unsuccessful you can also try clicking here --> https://support.apple.com/choose-country-region/media-services Select your country, then a product.