Charging more than the MRP

Location/place: Dhanbad

Dear Sir,
This is to register a complain against a retailer in my neightbourhood. He always sells products at a much higher price than printed on the packet. Example even a simple product like milk. Sudha milk is priced at Rs. 16 per 500 ml on the packet but he refuses to take that, he always charges a higher price than the MRP.
Kindly look into this and advice me what can i do in this regard.
Thankyou.