You are going to need to put in a ticket to have the Authenticator and old phone number removed. It is going to take some back and forth. They will send you an email (or ticket) asking to try to answer some questions to verify you are the account holder. DO NOT REPLY to the email. Open the ticket again, or open a new one, cite the first ticket number, then put in the info they asked for.
If you have more questions about the process the best place to ask is the WoW Customer Support forum. That serves as an Information Desk to help folks navigate the Support system, explain policies, explain services, etc. They are not GMs but there are lots of knowledgeable folks around and Blizz blues to help guide you. Just expect this will take a few days with ticket times.