We wish the stores were connected but unfortunately Apple, Google Play and Kindle store are all independent with no connections so a permanent purchase (like the upgrade) on one does not carry over to the other account. We are required to connect those to the iTunes/GooglePlay/Amazon account that bought the app rather than to our Word Chums account. You can find the upgrades under settings (top right on main screen)
Now in the case of Chumbot games you can get around it. You can start a few games on your paid app. As long as they get started on the upgraded version you can access them on any device. Thanks for your support!