Are these purchases that show on your iTunes account's (or an account that you've linked to the card) purchase history ? If they are, and if neither you nor anybody you've given access to the account did them, have you changed the account's password and contacted iTunes Support about them ? If not you should contact them : http://www.apple.com/support/itunes/ww or http://reportaproblem.apple.com or https://www.apple.com/emea/support/itunes/contact.html
If they don’t show on your account(s) (and if they aren't : About payment card authorization holds in the iTunes Store - Apple Support) contact the card issuer