I ordered LOOPY HD from iTunes and did not get my APP DOWNLOADED
Does iTunes sell LOOPY HD?
MacBook Pro, iOS 9.3.1, DOES iTunes sell LOOPY HD?
Loopy HD is an app for iDevices. Is that where you're trying to download it?
Normally, you log in to App Store using your Apple ID, click on the app price button, confirm you want to purchase it, then download it. That's why I'm confused by your title that you "ordered ... from iTunes".
If you explain in greater detail, I might be able to help more.