Hi there. Under no circumstances will Bungie forcefully unlink an account from a player's profile. You must be able to authenticate you are the owner of the account with the login credentials to unlink it. If you cannot, you'll need to contact Playstation Support to see what they can do.
If there's an unauthorized account link, that means someone else has had access to one or more of your accounts to be able to link it. We highly recommend you change your passwords and enable 2-factor authentication to secure them. [url=https://help.bungie.net/hc/en-us/articles/360048721292-Account-Security-Guide]Account Security Guide[/url]
See the [url=https://help.bungie.net/hc/en-us/articles/360049498031-Destiny-2-Cross-Save-Guide]Cross Save Guide[/url] for more info.
[b]From the Cross Save Guide:[/b]
[quote]All linked platform accounts must be authenticated in order to enable or disable Cross Save.
Players who can't authenticate connected platform accounts will have to contact their platform's support to try and gain access to the account. If that isn't successful, players may want to unlink their connected accounts they have access to and link them to another Bungie profile.[/quote]
If someone else has linked their account to your profile, that's a security issue you should immediately address as recommended. If you can't authenticate the account to unlink it, you can unlink your other accounts and link them to a new profile that you can activate Cross Save with.
[i]Note that to do this you'll need to link a dummy account from a platform you're not using (Playstation, Stadia or Twitch) in order to sign into your profile to unlink both your Xbox and Steam accounts.[/i]