Why is Apple charging me a unknown purchase?

This is a user to user only forum. We don't know you or what you may or may not be being charged for. First make sure you were actually charged for something as there are a lot of scams out there, which may suggest you were charged for something, when you weren't.

First thing do so would be to check your subscription to see if you were actually charge for something --> If you see an Apple Services charge you don't recognize on your Apple Card - Apple Support

https://apple.com/bill is the place to go to see all the charges related to your Apple Account.

Additionally, on your phone, you can go to Settings -> Apple Account -> Media and Purchases -> Purchase History to see purchases made in the last 90 days.