How do I remove apple icloud-mail after changing Apple-ID?

I have changed my AppleID to a gmail adress some time ago, and now I am trying to delete the old one, since I am no longer using it. The old was an iCloud adress, but it can't seem to be removed. When i search for how to do this, I only find solutions where a red removal button is shown, but this does not show on my phone. When i press the information-button behind the adress to be removed, it says "E-mail can not be removed. Use iMessage- and FaceTime-settings." And when i log in to my Apple-ID on the computer, i get a message about the iCloud being an alias, but not the option to remove it. I have talked to support about this, but i don't think i understood what he meant. Can someone please help?