I am trying to deregister the number of a stolen ‘phone. In following the instructions forwhen I have neither the devicenor the SIM Card, I receive a message saying a code has been sent and to please enter the code. To where was the code sent?

Hello OdinFraKanada,

Thank you for reaching out to Apple Support Communities! It sounds like you're wanting to deregister iMessage on an iPhone no longer in your possession, however you're unable to do so as you don't have access to the phone number.

Since you're unable to complete the steps in Deregister and Turn Off iMessage - Apple Support, we suggest contacting Apple Support for a closer look:

Get Support

If you haven't already done so, you may also want to consider changing your Apple ID password in addition to the other steps mentioned in the resource below:

If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

"Change your Apple ID password. By changing your Apple ID password, you can prevent anyone from accessing your iCloud data or using other services (such as iMessage or iTunes) from your missing device."

Take care.