Someone has already set up Teams for your Organisation

[Clarey]

Morning all, have just done the Contact help who suggested I come here. I am a freelancer and have my own website, it's just me, I own the domain. Got paid 365. However I can't use full functionality of Teams eg invite someone to a meeting. When I try to log in it says AADSTS50020: User account 'my email' from identity provider 'live.com' does not exist in tenant 'Microsoft Services' and cannot access the application '99adaf47-f643-4c0e-8117-15335c87ebda'(Microsoft Community) in that tenant. The account needs to be added as an external user in the tenant first. Sign out and sign in again with a different Azure Active Directory user account. 

It's only me in the organisation? Would be very grateful for some help. 

[#2]

Which subscription do you use? Including full Teams? Try using Teams on the web instead of the desktop app to verify if all is good. And when doing that either use InPrivate / Incognito browser sessions or separate profiles so no existing cached credentials are being accessed.

In case the web app works fine I suggest you sign out manually from the top right corner in the desktop app to clear some cache and refresh settings. Also look in your computer under "accounts" so you don't have any other accounts listed there that might try to connect. You can also remove and reinstall the app.