Not able to log into account on new phone

[NINA4]

Hi

i am unable to log into my o2 app on a new phone (username and password are correct). Even on website, I can login to O2, but when I go to My O2, it asks me for username and password again and also does not let me log in ( I get a something went wrong, contact us message). 
Any ideas how to fix this? 

[pgn]

Try an incognito or private browsing window or tab in your browser, @NINA4 - and log in using the Sign-In option at the top-right of the O2 website: https://accounts.o2.co.uk/signin

The phone app can be temperamental, needing the app to be uninstalled, the phone rebooted, and the app installed again from your phone's App Store - then it might work. Good luck, @NINA4.

[Oxonian]

@NINA4 

if the solution of @pgn does not work, I suggest that you try deleting all of your internet cookies and then give it another try.