We are sorry your app renewed without your knowing. Both App Stores send emails about a week to two weeks prior to renewal notifying you of the upcoming charge. We all get so many emails that often people delete it without even reading it.
Never fear, your App Store receipt has a "report a problem" link right on the receipt. Please contact your App Store within 24-48 hours and you should be able to get an refund from them as they have your payment information. Please contact us if you have any issues after that.