I was charged for an app I didn't buy.

I got a reciept for $14.98 for a free app and 2 in-app purchases within the app. I've never seen the app before in my life, and I have never made an in-app purchase either. I NEED to know how to un-buy the app–when I click the "report a problem" button, it just takes me to the front page for the iTunes support website at http://www.apple.com/support/itunes/. How can I remove the purchase and get the money back??? I've already changed my password, so I'm not too woried about being hacked (or whatever happened) again, but I am worried that I just lost 15 bucks. Fortunately, I have no active credit card with my account, so identity theft isn't an issue... I just want my money back.