Hello @Gavin,

Is this an iPhone by any chance?

This occurs due to iMessage, as the number doesn't automatically update when you port it over.

Try the following to see if it resolves:

1) Try turning off iMessage (Settings > Messages)
2) then restart your phone (by pressing and holding the on/off button)
3) tap Settings > Phone > My Number and confirm that it is correct.
4) If it is not correct, please enter the correct number)
5) then turn iMessage back to On (Settings > Messages)
6) go to Settings > Messages > Send & Receive and see if the correct number is displayed under “Start new conversations from:”

Mohammed