Email accounts on my iPad

BT say my difficulty (despite their expert help) in setting up a new BT mail account on my iPad (they are closing their previous BT Yahoo system and require me to change) could be an Apple settings problem, not a BT issue. I don’t know how to get help. I have the same account on iPhone and iPad. I have successfully deleted the Yahoo account and am without email, which is a problem while socially isolating. I am in my eighties and only moderately it literate. I went through the set up process in Settings/Accounts/Add Email Account. It said my details were inaccurate despite having them verified by the BT helpline and did it several times with care.

Any advice on what to do will be much appreciated.