If you got a message from Authy notifying you that, "This number was previously used for 2FA. A request was made to update that number," try these options:

• If you are the new owner of this phone number, you can ignore this message. It is a security warning aimed at the previous owner. 
• If you still use this number for 2FA with a website such as Twitch, Sendgrid, etc... check your email and cancel this request to change the phone number, or use the Authy app. If you no longer have access to the email linked to those accounts and can't install the Authy app, please contact Authy support

And how many times will this message be sent?

• The message will be sent 4 times.
• You may reply STOP if you like, to stop the next 3 copies of this message (there will be 4 warnings, to help make sure no hijacking of the number occurs).