cannot remove number from new (15 pro max) phone after old phone was disconnected

After the migration from the 12 to the 15 pro max i wanted to cancel one of the two numbers. ATT cancelled the old number, but it still shows up (in settings>Apple ID>settings and security) and will not let me delete it. I still have the old phone and did shut off iMessage and FaceTime as instructed but it made no difference, When I go online to deregister the old number it says it does not exist. I just want to remove the reference to the old number on the new iPhone as it is now defunct. Thank you