Can no longer send emails: Outlook wants me to validate my account but doesn't allow me to

Ive used my outlook account for already almost a year without a problem, but since this month, i can receive emails but not send them. I receive this message when try to send emails:

To continue sending messages, please sign in and validate your Outlook.com account.

This helps us stop automated programs from sending junk email.

But when i signed in the first time, it sent me a code to my mobile phone, which i then entered and it said it was wrong. But i did it twice and both times I typed it correctly...

I have even validated my account on outlook.com whereby they sent me a code via email (to another email address) which i successfully entered. But didn't solve the problem of being able to send emails.

Today, when I sign in, I don't even get the option of validating. So I don't know what to do...

Looking forward to hearing back from you,

Best,

Marlo