I'm not aware of any phone support for iTunes, but you can contact them via email via this page : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption
More than likely what has happened is you made an in-app purchase by accident and didn't realize it. Pretty common occurence. If you do end up calling, please be nice. The iTunes store isn't the one who charged you, it was the application and the developers are soley responsible for the behavior of their application.