Can't login to MS 365

I have had a 365 account for years, working fine on iMac. I want to install 365 on MacBook, but trying, 365 said my password is wrong (AFAIK I have never logged out on iMac). None of the iCloud passwords for account.live.com nor login.live.com nor microsoft.com worked, so on MacBook I asked to reset the 365 password. I passed the two-factor test and let Safari choose a new strong password. Then 365 asked me to login, but the new password I just set was rejected. I tried again, carefully copying the new Safari password I photographed, rejected. So I tried again to set a new password, but it said too many attempts, try again tomorrow. That was a few days ago. I went through the whole process again just now, same thing, locked out for another day. The biggest frustration is that Microsoft refuses to help without my first logging in.

Do you KNOW the cause of or the solution to this chicken-and-egg problem? Thanks!