See your purchase history in the iTunes Store on a Mac or PC - http://support.apple.com/HT204088 - Does not include purchases made by others under Family Sharing; those have to be checked from their accounts.
If you see ‘itunes.com/bill‘ or an unfamiliar charge on your bank, credit card, or debit statement - https://support.apple.com/HT201382 - "Before you contact Apple to request a refund for a charge you don't recognize"...
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.
Report a Problem - http://reportaproblem.apple.com - "Sign In for help with iTunes purchases made in the last 90 days"
Other ways to contact iTunes Support: