I've got an old unused key that I want to use, how can I redeem it now?

The key is from before rust was on steam. I’ve sent a ticket but haven’t heard from anyone.
So, is there any way I can convert that key to a steam-key? It would be very helpful if anyone knew how.

As far as I know

If you have not used the key itself to register any account, http://old.playrust.com/user/register/

If you have registered already, or you just did that, http://old.playrust.com/user/login/ to log in. Then click “Steam Key” at the top.