My bill

You've checked your account's purchase history : See your purchase history in the iTunes Store on a Mac or PC - Apple Support ?

If there are items on it that you don't recognise, and nobody else has access to your account and/or devices/computers and did them, then contact iTunes Support : http://www.apple.com/support/itunes/ww

And change your account's password : http://appleid.apple.com (What to do after you change your Apple ID email address or password - Apple Support)

If nothing shows on your account's purchase history, and they aren't temporary store holding charges (About payment card authorization holds in the iTunes Store - Apple Support) then contact your card issuer