Twitter appears to have disabled two-factor authentication for Google Voice numbers (2FA).
Although it is not the first firm to prohibit the use of fake phone numbers for SMS authentication, the change might be linked to CEO Elon Musk`s strong efforts to eliminate bot accounts from the network.
According to resources, the new behaviour appears to prevent users from using a Google Voice number to authenticate their accounts.
Musk has been vociferous about eliminating bots from the network since purchasing Twitter and taking over as CEO (a role he now claims he will retire once a replacement is found).
Although Google Voice was not mentioned in the article, anybody with a Gmail account may create a free Google Voice number, making it an easy authentication mechanism for bots, fraudsters, and spammers.
You should be able to update your phone number without contacting support if you set up your Twitter account with Google Voice authentication.
To delete that number and add your primary carrier line, go to Twitter Settings > Security and Account Access > Security > Two-Factor Authentication.