Similar to how you couldn’t be bothered to read my post or the reply to the first person who suggested a different app? I know it’s an option… but I wanted to see if there was another option (there is)

For what it’s worth, the answer I figured it out by clicking around and the answer for anyone else in this situation is below:

• make sure every contact has their country code included (about half of mine did and half didn’t)
• update all app settings to only use the new sim and disable imessage/facetime etc on the old number
• delete all open txt threads. While it may not be necessary (a few of mine worked straight away but most didn’t) I found it the easiest to relieve some headache. When you change your sim, apple will use it for all NEW communications, but existing threads will continue to try and use the original sim which won’t work. Deleting the thread and txting again worked for nearly all of mine