In-app purchase won't download

A couple of days ago, I was on my iPod touch (on a Wi-Fi network) and I was on this app (Tap tap revenge 3) and I tried to buy a track on there. It didn't ask me anything about buying the song.When I checked a couple of minutes later, nothing happened. I got charged for the purchase and that's it. I just checked my e-mail and that's how I found out that I got charged for something that I didn't get, so I've been looking all over the place trying to find somewhere I could report this to and I can't find it. So if you could at least give me a like to where I could get some help with this, it would be greatly appreciated. Thanks.