Subscription
I bought the pandora premium subscription and the first time it told me the store couldn’t process the transaction but now I’m being charged twice for the subscription and my Pandora still hasn’t updated.
Both purchases went through : See your purchase history in the App Store or iTunes Store - Apple Support , one isn't just : About payment card authorization holds in the iTunes Store - Apple Support ? If it did go through twice and shows twice on your purchase history : http://reportaproblem.apple.com (and check to see if it shows twice in Subscriptions : View, change, or cancel your subscriptions - Apple Support).
For not receiving it, have you looked on the developer's website for a help/FAQ section and/or contacted the developer ? If they can't or won't help contact iTunes Support via the above 'report a problem' site