According to TRAI (Telecom Regulatory Authority of India) regulations, sending messages on the DND activated numbers is allowed. However, it can only be sent when the receiver has signed up to receive your texts while signing up for your purchase.
Nevertheless, you can also use DND manager. Under this manager, you will just have to ask the user to send a message to your inbound number. This, in turn, works like an opt-in proof that lets you enhance your base. But this opt-in is valid for just 6 months.