It says my game account is already linked to another user
A Fortress W account can be linked to one Creta account only, and that one is already claimed by a different Creta account — usually your own older one.
So the first thing to check is whether you are signed in to the Creta account you actually play under. Signing out and back in with the right one resolves most cases.
If you believe nobody else should have it, contact us. Include the Creta account you are signed in with and the in-game name you play under; we can look at the link from our side. Please never send a password or a recovery phrase with it — those are never needed to investigate this.