Shopkeeper refusing to refund for a defective product, what can I do?

I bought an expensive smartwatch from a local electronics shop in Delhi last month, but it stopped working within two weeks. I approached the shopkeeper for a refund or exchange, but he outright refused, claiming it's not his responsibility once the product is sold. I'm feeling frustrated and don't know how to proceed legally to get my money back or have the product replaced. What are my consumer rights in this situation?