Stopping iPhone app from using Facebook login info
If you want to remove personally identifying data (for example tokens or whatnot) that the developer has stored about you in the Keychain on your device, you'll need to not only delete that specific app - but also delete any other app created by the same developer. I.e. other apps that share Keychain access with the problematic app will retain the data.

The developer also has the possibility of storing 2 bits of information unique for your device - the so called DeviceCheck API. The bits are stored at Apple and won't be deleted when you uninstall the problematic app and all other apps by that developer. The developer might have used one of those 2 bits to mean that the user is blocked from using the app.