Can't FaceTime or text one person

I tried to FaceTime a contact in my phone and I got a message saying "choose another phone number or email address to call "contact name" "phone number" in the contact card is not available for FaceTime. The contact was also unable to FaceTime my number. I tried sending an image which wouldn't send and sending a message results in a green text bubble instead of a normal blue one. Both of us are unable to FaceTime or text each others numbers but we can FaceTime and text other people. Before this our phones had no issues using our numbers to call and text each other. I think this is the second time it has happened within the year. FaceTime and messages work then they suddenly stop, then it goes back to normal again.