How to regain control of my Microsoft account?

Question

Right, I haven't got a clue what's going on here, so bare with me.

I have a personal domain name and email address on that domain - for clarity let's say these are nickstadb.foo and ******@nickstadb.foo. These are 100% mine, 100% personal, and have never been owned, operated, managed, or used by anyone else, ever.

I have a Microsoft account with the same email address, that I rarely use. At some point I may have used it for Xbox Live, well over a decade ago. At some point about 8 years ago I purchased a Microsoft office licence with it.

At some point, Microsoft decided that an organisation manages this account.

When I enter the email address ******@nickstadb.foo to sign in, I'm presented with two options: "Work or school account. Created by your IT department", or "Personal account. Created by you". To reiterate, this account has always been 100% mine and has never been associated with any organisation. I do not have an IT department or an administrator. I am the sole owner and administrator.

When I attempted to sign in, neither option accepted the password in my password manager.

I figured the password may have been wiped/reset due to a security incident or simply because I haven't logged in for so long. I tried to reset the password using the "personal account" option and I was told that I was not enrolled for password reset and would need to contact my administrator. I tried to reset my password using the "work or school account" option and I was told the same.

Eventually I found a web page buried somewhere in a Microsoft website that offered to email my administrator for me to request a password reset. Guess where that email was sent to? Yes, ******@nickstadb.foo.

Again, I can't stress this enough, I am the sole user of this email address and domain. It is not and has not ever been owned by, operated by, or associated with any organisation. I am the sole administrator and always have been. I have never had an IT department.

Fortunately, I was able to sign in to the "personal" account using the authenticator app which I must have set up at some point. From there I was able to change the password, but only for the "personal" account. Only my administrator, who happens to be me, can reset the password for my "work or school" account, but I need to log in to reset the password because my administrator (me...!) hasn't been enrolled for password resets. Only my administrator, me again, can reset the password for my "personal" account if somehow the password in my password manager becomes invalid again.

How can I regain control of my "work or school" account? Can I delete this account or make it entirely a personal account, given that nobody has ever managed it apart from me and it has never been associated with any organisation?

P.S. Not sure what tags are relevant - this is a Microsoft account issue but there was no tag for that.