i have the save problem in UAE, the problem comes from the LTE network. the problem solved as the following: 1- make factory reset and complete format 2- after formating and while activating your phone , you will get message from your carrier saying that there is a carrier network update, this update is for the LTE . Don't update the carrier and keep using normal or 3G, then the problem will solved. note: before update you will see you mobile like this: setting -general - cellular - cellular data & Enable 3G. after : setting -general - cellular - cellular data , LTE, .......etc.