what if you don't have the phone number to receive the six digit code?

Salutations, 

We understand that you’re asking about deregistering a phone number from iMessage, though you don’t have access to the phone number to receive a verification text. You also consulted Deregister iMessage on your iPhone or online for assistance. 

If you no longer have that phone number assigned to a device, whether it be a new or old device, then there wouldn’t be an issue where you can’t receive SMS/MMS messages. Can you tell us a bit more about what issue you’re encountering that leads you to work at deregistering the number? 

Thanks. 

Hello,

I am facing the same issue. I'm about to return the phone to my previous work and I've reset the phone. How can I deregister the phone number without having to get the code through the old phone number?

Thanks!

I am also in the same boat. I erased and deleted the work iPhone which I returned. Removed it from settings. Still showing my previous work phone number under “reachable at”. Along with my new number and Apple ID. iMessage is set to only my new phone number along with FT. Will not let me remove old work number without the code. There has to be a way to remove it 😑.