I ended up switching to NumberBarn from Google Voice. They're a bandwidth.com reseller. I usually don't have a problem with receiving codes from services, but there are the rare places that don't allow VOIP numbers.
You don't have an account with Mastodon. You have a Mastodon account with sdf.org. Their mailing list that sent the email and the Mastodon instance they run are probably separate systems. You can forward your email to membership@sdf.org and ask to be removed.
I ended up switching to NumberBarn from Google Voice. They're a bandwidth.com reseller. I usually don't have a problem with receiving codes from services, but there are the rare places that don't allow VOIP numbers.