I recently upgraded from a iPhone 4s to an IPhone 6s. After attempting to restore purchases it said it completed but after multiple attempts the upgrades I have purchased do not actually get restored. And yes, I am using the same iTunes account.
If you are using the same Apple account and the same app (note iMtG purchases do not transfer to Plus yet), then talk to Apple to get your money back as the problem is with their server infrastructure most likely (Restore Purchases works for other people and is tested by Apple as part of App Store release process so the app is fine), and I hope you will purchase again.
Thank you I got it all sorted out!
What was it? Yours is a frequently asked question so it would be good to know what one of the the answers is ;)