Hi there, I am Cris and will be glad to assist you.
What Android phone do you have?
OK, let's uninstall the app and de-register your phone from your Amazon account.
First use the link I have provided to get to the Kindle Manage Page. When you log in click on the "Devices" tab.
Click on your phone from the list and click on "Device Actions" select deregister.
Go to your phone and remove the app of the phone. Then reinstall it again from the Google Play store. Then sign in with your Amazon account to register again.
Let me know how you make out. If this answers your issue/question please take a moment to rate my service and submit at the top.