@Anonymous Considering you are locked out and cannot login as you have your old number mentioned for MFA. Your admin should be able to change the phone number for you. They can go this this place and change it to your current phone number :
This should unblock you if you are locked. However if you can login and just need to change your phone number. You can use Myapps portal to edit your number.
-----------------------------------------------------------------------------------------------------------------
If the suggested response helped you resolve your issue, do click on "Mark as Answer" and "Up-Vote" for the answer that helped you for benefit of the community.