Q: Unable to receive calls in iOS 8.1.3 on iPhone 6 Plus (AT&T)

I've been running iOS 8.1.3 (using AT&T) since its release but only in the past couple of days I have begun to experience not being able to receive calls. I will get a single vibration that makes me think a call is coming in but nothing appears on my screen. I go to unlock the phone and the green bar on the top of the screen says "Return to call 0:00" but nothing happens and it almost immediately goes as a missed call.

I've done soft resets on my phone and tried testing from different phone numbers and it still persists.

Is anyone having this issue and if so, can please help? Thank you