Aquafina — overcharged for water bottle more than mrp by bhimas restaurant putalapattu

Hi
I have been to Tirupati and while returning back the bus stopped at a restaurant named Bhimas at Putalapattu, Chitoor. I bought a water bottle and they charged me inr 30, but mrp was 20. I asked them about this then they said they charge like that only. I told them it is against the rules, but still they charged inr 30. I request you to take strict action against them.
I have bill also with me and their GST registration is 37AAPFB2628C1ZL.

Regards,
Vinay