@superdriks you didn't receive the email because you never verified your email when you signed up (aka actually clicked on the link in that email that you show in your picture)
therefore the email is not associated with any account (which is why you were able to create a new account with the same email).
Make sure you verify your email on this new account so you don't lose access to this one too.
As for the steam account part, from what i've seen, plutonium doesn't really do manual steam unlinking. There is too much potential for abuse and all the things you would need to provide to prove you own that old account would be the same things you would need to log into it and unlink steam yourself.
Your best option for that issue is to remember the password you used on that OG account and unlink it once you log in.
