Help needed apps not loading

HELP NEEDED

Ok everyone it's a long shot I know but recently I have downloaded 2 new apps on my phone.

Both require a log in which won't work.

I have tried everything. I have:

*confirmed details are correct

*ensured app and software are up to date

*registered properly

*updated my software

*cleared caches and data
*uninstalled and reinstalled the app
*checked the correct version is running and settings are to AU/NZ
*restarted phone contacted Samsung AND
*spoken to the developers of both apps who have no idea what's happening

Neither app will recognise my username so I can enter my password and get in.

There must be something stopping the apps recognising my username and I suspect it's an Android issue as BOTH apps work on an Apple device and the login works fine.

Do any of my techie friends therefore have any idea what may be causing this and how to fix it please? I'm paying for both but unable to use them.

Thanks in advance.