thanks for the feedback. I'm really sorry that you are having such a bad experience with my app.
Unfortunately, I do not have an own licensing system but solely rely on Amazon telling the app that you actually purchased the pro version. This seems to have become very unstable in the last few weeks. As I'm unable to reproduce the issues using the tools Amazon provides for testing, I'm pretty much out of options here.
Up until now, deleting all official Amazon apps from the device (i.e. App Shop and the Amazon shopping app) and reinstalling them, seems to have fixed the issue for all customers that ran into it. After doing this, either reinstall Deliveries too or force a new license check by pressing the "Buy pro version" button and choosing the app shop. If the check is successful, the dialog just disappears and the ads will be removed. If you see an Amazon style purchase dialog instead, it didn't work.
If the issue persists, demand a refund of your initial purchase from Amazon customer support (I have no control over this).