If you tried the Reset Network Settings, and that didn't work, you may as well try a hard reset too. Hold the top power/sleep button and the home button at the same time until the Apple logo appears, then release. If this does not correct the problem, you will need to either have your carrier look at it or take it to an Apple Store Genius Bar. It could very well be a carrier issue. Is your wifi or cellular signal strong? A weak signal could do that. Anyway, good luck!
Sent from my ancient but trustworthy iPhone 5.
12-22-2014 07:40 AM