Not able to receive SMS in GSM GPRS SHIELD FOR ARDUINO SIM900A UNO LEONARDO MEGA

Hi,

I am using Arduino Uno R3 ATmega328P ATMEGA16U2 (http://www.amazon.in/gp/product/B015C7SC5U?psc=1&redirect=true&ref_=oh_aui_detailpage_o07_s00)

with GSM GPRS SHIELD FOR ARDUINO SIM900A UNO LEONARDO MEGA (http://probots.co.in/Manuals/GSM%20Shield%20-%20Manual.pdf).

Problem:- I am not able to receive SMS (when i send sms from my phone , the message is not getting delivered to shield) i am using the sketch given at https://www.arduino.cc/en/Reference/GSMSMSRead for receiving SMS.

Note: - I am able to make a voice call, Send a sms and receive a call using the example sketches given in arduino IDE. Only problem is with receiving the SMS. Please help.