Tasmac — Overpricing of liquor above MRP

Me and my friend went and bought four bottles of Red wine from Elite Tasmac shop Injambakkam. I was charged Rs. 50 excess per bottle above the MRP. On asking about the overcharging, the guy in the counter said, it is like that. On asking for bill he said there is no bill and the charge slip is sufficient. Even after so much of complaints these people continue to loot money like this, is there any mechanism to stop these practice. I would really want to understand and would like to have strict action taken on this matter.

Hoping to hear from you soon.