iPad mini 4 FaceTime is not ringing.

Open Control Panel by swiping down from the top right corner. Check for the Mute icon. It appears as a bell. If it is a red bell with a slash on a white background, the device is muted. Tap the icon again and it should change to a white bell on a dark background. You should now hear sounds.

Go to Settings>Notifications>FaceTime and make sure that you have a sound set and Notification are on.

Glad you got it all sorted out.