Why are my iPhone texts going to my boyfriend's work number?

My boyfriend and I recently upgraded from iPhone 12s to iPhone 16 Pros. I have two numbers saved for him: his mobile and his work number. I usually text him on his mobile, but ever since I got the new phone, some of my texts are going to his work phone instead. I've tried blocking the work number, deleting it, and attempting everything I can think of, but nothing seems to work. His work number still appears, and the contact name shows up as "Maybe Clay."

This situation has become really frustrating because I have no way of knowing if my texts are actually being sent to his mobile number. I would greatly appreciate any help with this issue.

[Re-Titled by Moderator]