Can no longer log in with username

Posted this before but it was pushed aside as an account issue. It is not an account issue. When I type in my email and password, the new launcher allows me to login. But when I type in the same password but use my username instead (as the launcher says I can use both) it no longer allows me to login. This was never a problem prior to the launcher update. This is a huge issue for my brother who cant migrate his premium account because we no longer have the Transaction ID and Mojang Support cannot help. This needs to be acknowledged as my brother can no longer play.