Should I have to pay to change my gamertag under this circumstance?

Around 12 years ago, I bought an XBOX 360 to use offline only and had to install an update to get a game to work, so I signed in with my msn email address. I don't remember even having to choose a gamertag at the time. Fast-forward 12 years to today...I
recently upgraded to Windows 10 (hesitantly) and decided to try Sea of Thieves. I used my old MSN account because that's the only Microsoft account I have, and when it logs me into the game, I notice that it's using my full name as my gamertag. So a friend
tells me I need to go change it. At that time, Microsoft tells me that I have already used my one-time free gamertag change (huh? I never used XBOX Live, much less changed my gamertag) and that I'm gonna have to pay $10 to get my real name off my gamertag?

:)