The issue you're having is because you have a different Steam ID linked than the one you think you have linked. The one you keep authenticating to, the one you "know" is yours, is a different one from the one you actually linked. Most likely, when setting it up, you used an email to authenticate to Steam at the time instead of your Steam username, and as such, it activated an older Steam ID that you may not even know or remember you had. As long as you're the one that set up Cross-Save and authenticated to that Steam ID, and it wasn't someone else, then the following should help you out. Please go to Steam's website, log out, then on the log-in page, go through the steps of having forgotten your username/password. Once you enter the code from your email, Steam should show you every username attached to that email. Ideally, since you, yourself, would have authenticated to it, it would have used the same email and password you normally use, so it should be connected to that email. If the other username shows up there, you should then be able to authenticate to it using that username and your normal password, since you did so accidentally previously. However, if the username is not linked to your email, and you don't see the second account there, then, unfortunately, you'll have to work with steam to recover the Steam ID. Steam will not be able to assist you in unlinking the account, so you need to specifically tell them you're trying to recover a Steam ID and you only know the display name. If you just say you're trying to unlink it from Bungie, they'll just send you back here, and Bungie cannot help you recover a forgotten Steam ID, nor will Bungie forcefully unlink the Steam ID or make changes to Cross-Save.