choose another phone number or email address to call so and so, then proceeds to tell me the number that I'm trying to call is not available for FaceTime in the contact card.

So ever since last year, every time I try to FaceTime this specific number on my phone it says "choose another phone number or email address to call this person, then proceeds to tell me the number that I'm trying to call is not available for FaceTime in the contact card. It only does it for this specific number. It does it on their phone as well. They even got a new phone and it is still not letting us FaceTime. I've tried everything from restarting my phone to turning off FaceTime and turning it back on, and deleting the persons contact card and re-entering it. I don't know what to do anymore