The support article If you see 'apple.com/bill' on your billing statement - Apple Support and the related article Get help with charges from apple.com/bill - Apple Support explain how you can check your iTunes and App Stores purchase history, cancel subscriptions (remember that these need to be canceled at least 24 hours in advance), and track possible sources of unrecognized Apple charges you may see on a bill. These may be purchases by Family Sharing members, others sharing your card (such as a spouse or partner, or a second Apple Account you have; you may not see a receipt).
The article also provides a specific link for contacting Apple if you cannot trace the source of charges, e.g., if you subscribed to something directly with a third party, see: About purchases not billed through the App Store or the App Store’s In-App Purchase system - Apple Support instead. In that case you need to work directly with the vendor, not Apple.
If you use Apple Card you may find this document helpful too ➞ If you see an Apple Services charge you don't recognize on your Apple Card - Apple Support
● If neither you, nor Apple, nor a Family Sharing member can account for a charge and it ONLY appears on a bill for a charge card you alone control, you may have been the victim of card fraud. Contact your financial institution immediately. Any “refund” would have to come from them, not Apple.
● Small amounts of ~$1 may be an authorization hold that will be refunded (pending charge ➞ How apps, content, and subscriptions from Apple are billed - Apple Support ).