I reached out to Help Desk yesterday, AGAIN and this is what I was told (word for word from my case transcript). I was told by another agent, to enable TFA with my email address.
"Now you need to wait for 24 hours, after that just disable the login verification and try to enable it again and then you can update anew phone number."
When I asked for clarification on how turning TFA on and off again was supposed to help since my old number is still attached. He told me it would take 24 hours. See his response below.
"Previously TFA was enabled with old phone number. You change the login verification method from old phone number to new number and now it will take 24 hours for old number to be deleted from the account. After 24 hours, disable the login verification and enable it again using phone number method and it will allow you to add new phone number."
I don't understand this at all. We used to be able to modify and delete old number. I don't know why this was changed. It has caused people nothing but problems. I am going to try again tonight and if it doesn't work, I was told to reach out to help desk AGAIN.