Titan Company — Exorbitant charges for watch battery replacement

Address:

Titan showroom Vidyaranyapura Bangalore

I got my watch battery replaced at Titan showroom in vidyaranyapura. They charged me an hefty price of Rs 400/ for replacing the battery. We were shocked after hearing 400 Rs for replacement. We asked why are you charging so much for a battery replacement, the person replied it is original cell and it will come for 4 years. We asked for the warranty but he replied waranty is only for 1 year but the battery works for 4 years. The person didn't give any bill for this service. That means he's not paying GST to government. Is Titan cheating both government and the customers.
Titan need to answer this.