I can't change the phone number on iMessage, so I cannot send SMS messages
I was recently in the US and got a phone line there. Now that I'm back home, I can't use iMessage because it is linked with the US line. No matter what I try I can't remove that phone number or add my local number.
I've tried the steps here Deregister iMessage on your iPhone or online - Apple Support and here https://selfsolve.apple.com/deregister-imessage/ and still nothing.
iPhone XS Max, iOS 12.0.1