Hey there! You cannot unlink an account without being able to authenticate to it. Bungie will not unlink it for you. You'll need to contact Xbox concerning recovering the account if you wish to gain access to it to unlink it. If that is not possible, you will need to move your good accounts over if you wish to cross save. You cannot unlink an account while signed onto it so you will need to create a free platform account and have it linked to your profile. All emblems tied to your current Bungie profile will not carry over to the new one. It is also not recommended that you give your console account information to anyone. I highly suggest that you enable some extra security measures to prevent unauthorized access such as 2FA. https://www.bungie.net/en/Help/Article/12718