Why are some of my GSM modules not taking commands?
I am owner of this blog whose link you shared, so first of all, I am felling happy that you got something out of it. Now secondly, this code you got from my post is incomplete. 

You need to buy that one in order to get the complete code. The code I designed is using AT commands but the above code which you have mixed with your own code is using the Arduino library that's why it's not giving the correct results.

So, either use the complete code from my website or use the Arduino library code only because it has the commands for checking the response, you don't need to use my code to get the response.