I struggled for 2 days to resolve this. And the solution was so simple. I resolved the issue accidentally. Besides following all the recommendations (except the hardware part) on different online forums I was exhausted. Doing nothing, I started making a backup of my cell phone with an idle mind. And there I found an option to reset your network. I have Sony Xperia Z3 Dual. You should try this. Go to Settings -> Back up and Reset Scroll down Go to "Network Settings Reset". Then reset your cellular network. And bingo. It worked for me. I was able to make calls and use my cellphone in normal mode. Please let me know if it worked for you. I can guide you for some more tricks.