You can view your account's full purchase history via your computer's iTunes : See your purchase history in the iTunes Store - Apple Support
Or on your phone you can view the last 90 days purchases via http://reportaproblem.apple.com
If you didn't purchase the item(s), and nobody else has access to your account or devices/computers and did it, then contact iTunes Support, either via the above 'report a problem' site, or via http://www.apple.com/support/itunes/contact/ (click on Contact iTunes Store Support on the right-hand side of that page)