MS games linked to someone else's Xbox account

I have recently been playing some MS games as a Guest, but decided to login. I have had a hotmail account for years, so know my user name and password. The login prompted to link to an unfamiliar user name, I declined to link to it, but it did anyway.
Now it appears that my games are linked to someone else's Xbox, complete with his friends etc. I have no desire to use his/her account or lock them out of their games, nor do I want them to get hold of my ID (password immediately changed). I cannot locate
anywhere I can send an email/web form to MS to have this fixed. I doubt if belongs in this forum, but it's the closest thing I can find that may help. I find it amazing that the system will auto link to someone else's account, despite declining the match.
Not secure and not good enough that MS are uncontactable for situations like this. Thanks

:)

 

Cannot sign in with Microsoft account

When I try to log in to XBox One with Microsoft account it says my account is already linked to another device and will not work. Works fine with someone else's account

 

Error after update

I was not using someone else's account I just presumed that because I had error 8c020007 that the xbox was linked to another account . I have tried today removing and replacing the hard drive, clearing the cache , reformatting the hard drive, reinstalling
my account, removing and reinstalling updates. Is there anything else I good do

 

When you create an xbox account for the first time it gives you a random gamertag. Is that what happened?