My Xbox won’t let me sign in

My son has been trying for two days to sign into his Xbox but it won’t let him sign in with his original information. He can’t play any of his games and even after changing the password etc and verifying the account so many times it still won’t allow him to sign in. I can sign in on the Microsoft account online absolutely fine but it won’t work on the Xbox. Can somebody please help. Thank you.

:)