[2021] You cannot link a steam Account different from the previous one

When did you unlink the accounts?

The only thing I can think of is that it's still in the wait period after you previously unlinked them. Other than that there is nothing more I can suggest but to wait for Support. They are inundated with tickets at the moment and there's a longer delay than we would like with getting replies to users, but please don't send further tickets/emails as that will just delay your ticket even more.