Tasmac — Charging the prices above MRP

I bought liquor from Velachery Tasmac Elite shop, they are charging Rs.40/- extra above MRP. When I asked what are these charges are for, they are responding very rudely and swiped my card with extra Rs.40/- without my permission. It's totally unacceptable to charge extra money above MRP and now even the prices are increased still they are getting these extra Rs.40 for each sale of bottle. Govt if not capable to resolve this, better they can privatise this sector.