FaceTime connection issues with long-term contact on iPhone SE and iPad

I cannot connect with a long term contact with my iPhone SE or iPad. A message comes up saying their information is not on the contact card. Also sometimes the message reads "Can 't place call because number is not registered on WhatsApp". What's WhatsApp got to do with it? My contact does not have WhatsApp anyway, that's why we video call on FaceTime.

[Re-Titled by Moderator]

Original Title: FaceTime problems