To remove an account from a Bungie profile you need to be able to authenticate it, so you'll want to work with Microsoft to regain access to it. If you can't regain access then it cannot be unlinked from that Bungie profile. As you don't have cross-save enabled, you could move your accounts to a new Bungie profile using a by creating a throwaway account on a platform you don't have linked (ie Twitch) and using that to unlink your accounts. This will mean your Bungie friend list/redeem code emblems/partner rewards etc would be lost though.