Bungie does not have your personal login information. Bungie does not store your login credentials, nor can Bungie verify your account ownership with anything other than your ability to authenticate to an account.
Bungie will not forcefully disable Cross-Save, nor will Bungie forcefully unlink one or more accounts just because you claim they're not yours.
The Cooldown for Silver purchase will not be reduced or removed, and once it has been waited out, you'll still need to authenticate to ALL linked accounts in order to disable Cross-Save.
Again, if you cannot authenticate to them, then, unfortunately, your Cross-Save will remain as it is.
This forum is the contact point for assistance concerning your Bungie.net profile as well as Destiny 1 and Destiny 2.
Bungie does not have an email you can contact for support concerning this, as, again, this is the point of contact.
Bungie will not forcefully disable Cross-Save or unlink an account just because someone claims to be the actual owner and the 'other account' on the profile was put on by a hacker.
All platform accounts linked to the profile have access to the Bungie.net profile. If one or more of the accounts is or isn't yours as you claim, then, yes, they'll continue to have access.