Number in phone settings is different to phone number from SIM card and won’t save changes

When I got a new SIM card I transferred my old number over but in the settings of my phone it shows a different phone number. My old one I still use with my new SIM card works fine and when messages try to get sent to the phone number in settings it fails to send as it’s officially an unregistered number but I can’t seem to change the number because whenever I press save to save changes it just ignores my changes and keeps the same number it displayed before.