If you’ve run into problems with making or receiving calls after updating to iOS 7 then you are not alone. You might find that people are trying to call you, but your iPhone is not ringing, or perhaps you are unable to make a call. Some people report calls apparently connecting, but the line seems to be dead and they can’t hear the other person. Assuming you’re not just in a dead spot (try making the call from another location), there are a few things you can try.

Potential solutions:

• Go to Settings and toggle Airplane Mode on for five seconds and then turn it off again.
• Make sure that Do Not Disturb in Settings is not turned on.
• Go to Settings > Phone and make sure Call Forwarding is not turned on.
• Go to Settings > Phone and check under Blocked.
• Make sure you have the latest carrier update by going to Settings > General > About. If there’s something available then you should be prompted to download it (make sure you’re connected the Wi-Fi and your mobile network).
• Make sure there isn’t another iOS update by going to Settings > General > Software Update.
• Try removing the SIM card, make sure it’s clean and replace it carefully.
• Try resetting your network settings via Settings > General > Reset > Reset Network Settings.
• Go to Settings > Cellular and try toggling Enable LTE and/or Enable 3G.
• Contact your carrier and make sure there’s no problem on network

If everything fails try to Factory reset

I don't take responsibility if anything goes wrong during the process!(chill it won't )