My User name was changed by MS , I can't return back to the original one

That depends on whether you're using a Microsoft account or a local account.

Your username is tied to your Microsoft account name. To change it:

1. Go to the Microsoft Account Page: https://account.microsoft.com
2. Sign in and navigate to Your Info.
3. Click Edit Name, update your first and last name, complete the CAPTCHA, and click Save.
4. Restart your Surface Pro to apply the changes.

Note that your old under c:\Users will not be changed.

if Your account is Local You can change the display name using either the Control Panel or Local Users and Groups.

Hi Lucio. Thanks for posting to the Community. To change to your desired User name, there are few ways depending if you are using a local account or Microsoft account.

If you are using a local account. Open Settings app>Accounts>Your info>Manage my account or Change account name>click it and enter the new name.

If the issue still persists, I suggest you to try doing a wipe/clean install of Windows on your surface device. Hope this helps, but if you have more questions feel free to reply.

Best,

Res