Hi,
My first suggestion would be to find out who hacked into your account.
Go to
https://account.live.com/Activity and review the account activity list. See some logins you don't recognise? From a country you've never been to? If so, click on the button "This wasn't me" for those logins.
I get that you have 2-factor logins enabled. That's a good thing. Still, I'd recommend that you change your password (again), just to be on the safe side. This should log out all active sessions, including those from someone hacking into your account.
Finally, I'd strongly suggest getting a proper business email account instead of using Outlook.com for critical business email. A business email account will give you access to a real support department who can help you much better. If you want suggestions for a good business email host, just let me know.
-peviha