Bests & Worsts Reviews from Amazon

I bought the upgrade for $8.99 and it downloaded and worked fine for one day... The next day after I started it for my son and he got frustrated enough I figured out that it wouldn't let him get past letter D... I thought it was weird but I seen a button that said restore but it stated I hadn't purchased the upgrade but I have the receipt to prove it. I'm currently trying to contact the developer to see what they can do for us. My son has autism and there's not many things that will keep his interest but I could that this does... please help me because I need this to help my son learn.