India Post — Not receiving otp to the mobilefor applying gds ap post

I had applied for ap post gds previously, but recently I got message for( the mobile number which i had used for the registration) re-apply of the options. I have been trying to apply but in ap post webpage it is showing as " sms sent to the registered mobile number" but I am not receiving message. Please help me. I am having good cgpa to get this job