iTunes charged me without buying anything
iiTunes charged me on music that I did not buy, how can I get my money back
iPhone 5, iOS 9.3.3
Does it show on your account's purchase history (if you are a family organiser in family sharing members purchases will be charged to you if they don't have a balance on their own account) : See your purchase history in the iTunes Store on a Mac or PC - Apple Support ?
If you've changed/added payment details you will have received a temporary store holding charge (to check that the details are correct and valid) which your card issuer should automatically remove within a few days or so : About payment card authorization holds in the iTunes Store - Apple Support
If it's an actual charge and shows on your purchase history and you don't think that you should have been charge, contact iTunes Support : http://reportaproblem.apple.com or https://www.apple.com/emea/support/itunes/contact.html