After a long dig I found that on 19 July, 2016 due to some error or updation at Apple’s end , the didRegisterForRemoteNotificationsWithDeviceToken method would not be called even if every condition like Internet connection , Device and the methods used are perfect.
Refer to this link for confirmation https://forums.developer.apple.com/thread/52224
To verify please have a look in your other apps too.
I had wasted my several hours but hope it helps someone.
Thanks.