Why can't I answer my phone?

This took me forever and i still don't know how it happened but, go to you SETTINGS, then go to APPS should be under the category DEVICE but it shows all the apps on your phone, then scroll down to the app that you use to make calls should simply say PHONE (side note make sure this app is set to DEFAULT), click on it and scroll down to where it says NOTIFICATIONS, there make for sure your BLOCK ALL option is off and at least TREAT AS PRIORITY or ALLOW PEAKING option is ON... Hope This Help You Or Someone Else... It's What Happened To Mine I Don't Know How And It Sucked...