Hi ​@Mummabear93.

Thank you for your post.

I am sorry for the inconvenience caused. Can you please follow these steps to do a network reset on your device;

Go to Settings. 
 Tap Phone. 
 Tap My Number. 
 Use the delete button to remove the old number. 
 Use the keypad to enter the new number. 
 Tap Save. 
 1. Go to Settings 
 2. Messages 
 3. Turn off iMessage. 
 4. Go to General 
 5. Reset 
 6. Reset Network Settings. 
 7. Once the iPhone is open. 
 8. Go to Settings 
 9. Messages Turn ON iMessage. 
 10.This will recognize the new sim and have it verified. 

Thanks,

Marquerita

The iD Mobile Team