The most common reason an iPhone stops ringing when you receive a call or text message is because your ring / silent button is turned on. Accidentally activating the mute switch is especially easy on newer models, such as the iPhone 6 or 6s. The ring / silent button is located on the left hand side of your device above the volume buttons. You will know if it the button is on mute if it is in the down position and you can see a small red line.
If your silent button is not on mute then check your Ringer volume by going to your Home screen and pressing the top volume button.
If your carrier pushes a carrier settings update, the iPhone will automatically prompt to install the update. Tap Update when the dialog box appears.
You can also check for a carrier settings update manually. Follow these steps to see if a new carrier settings file is available:
Carrier settings on the iPhone are stored in a file containing the configuration for cellular data and calling. Carriers, such as AT&T or Verizon, may include settings for calling, messaging, personal hotspot and other items in this file.
Your iPhone's IMEI (International Mobile Equipment Identity) is used to register your device and is sometimes required for technical support. It is also sometimes required to unlock your device. There are several ways to find your iPhone's IMEI: