Some company that offered services to us used Azure AD for their authentication into their portal, so when you registered with them it actually created an Azure

Some company that offered services to us used Azure AD for their authentication into their portal, so when you registered with them it actually created an Azure AD tenant. The user was not aware of this, but this started to become a real headache not only because users could apparently create Azure AD tenants out of nowhere, in some weird way I still don't understand, but certainly through user interaction, other users that had nothing to do with that portal also got added into this Azure AD! It took some shady workarounds to get control over this rogue Azure AD tenant and clean up the mess it caused. At this point we keep the Azure AD around not because we want to use it, but to stop anyone else from creating one with one of our domain names.