iPhone keeps defaulting to NZ number after removing eSim

So my partner and I used esims while on holiday, and when we got back, my phone keeps getting confused and tries to message the NZ number. I have removed the number from their contact, deleted the number, blocked the number, removed the esims from both our phones and created a new contact with their regular number, but nothing has worked. 75% of the time when I go to messages, it defaults to the NZ contact with text as the option, and whenever I receive a text, it will be from both numbers. Usually, if I close messages and reopen it, it will temporarily fix it but this lasts until I receive a text. How do I fix it so the NZ number stops showing up?

[Re-Titled by Moderator]

Original Title: Used esim on holiday, got back and now phone is confused on which number to text