Use this link to read about how to "See or cancel your subscriptions" - https://support.apple.com/HT202039
For unfamiliar charges work your way through 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
Prime suspects for unusual charges are subscriptions and purchases made by family members under Family Sharing (if applicable). These will not show in your purchase history but may appear on your payment card. You need to ask other Family Sharing members about those.
"If the subscription that you want to cancel is not listed", click here --> https://support.apple.com/HT212052
If you still can't find a subscription, contact Apple Support using the link at the end of the support article.
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 recognize it and have canceled the subscription and wish a refund: Apple's terms of purchase in the USA are, "All Transactions are final" (https://www.apple.com/legal/internet-services/itunes/us/terms.html ), but some countries have different laws so check terms for your country at: https://www.apple.com/legal/internet-services/itunes/. If sales are final then it is Apple's decision if they want to grant a refund. You can always ask, and people do get refunds on a case by case basis, but Apple can also say no.
Click on this link to read about how to "Request a refund for apps or content that you bought from Apple" --> https://support.apple.com/HT204084
If you still have problems, click here --> https://support.apple.com/choose-country-region/media-services Select your country, then a product.