Same thing happened for me, LG k10. I had to reset my phone. Then it worked BUT Once I backed up my data to reinstall my apps it started doing the same thing. So I reset my phone AGAIN this time not backing up anything and made a new Google account and its working now. Hope this helps.
I was having the same problem with my LG Phoenix today. I resolved my issue by backing up all my info to my sd card, removing said sd card, doing a factory reset, inserting my sd card back in on start up, downloading all my information back, and voilá! I am now receiving calls! I hope this works for you all!!
Here is the fix! I called AT&T and they said many LG customers are having this happen. Go into your apps and select the Drive Mode app. Clear the data and clear the cache. Then disable the app. When it asks if you want to go back to factory settings say yes. Turn phone off for several seconds. Turn it back on and the problem should be fixed. Hope this works for you!