I cannot FaceTime a certain contact?

Okay so I have an iPhone 7 and the other contact I am trying to FaceTime has like a 6 or 7 as well. We have FaceTimed in the past, and both live in the same general area and are using the right international code. Everytime one calls the other, you receive the call, but it does not connect. I did notice a question mark in the FaceTime box. We both have updated settings and is connected to a reliable internet source. Please help!