Can you access the internet such as from the browser when you are not on WiFi? WhatsApp needs an internet connection. If you don't have a data plan and need WiFi to access the internet, WhatsApp won't work work outside of WiFi.
Not sure if this applies to you, but I did get onto a WiFi network that actually blocked WhatsApp. I'm not familiar with your country, but it is possible for carriers to block certain apps. Someone else will have to confirm this. I don't know of any WhatsApp users in India.