Bill error on iTunes

I tried to sign up for a free one week use of the app Insight Timer via iTunes on my phone. I was charged $59.99 for a year's subscription on my debit card, even though I was unable to use the app at all, and deleted it from my phone. How can I get a refund to my debit card? I couldn't find a way to contact the app people or iTunes about this, and I don't want to subscribe to this app! Help!