Nothing can be charged over MRP. If old MRP is printed, he had purchased it in old price, so they should have sold it in , what MRP is printed. u could ask for a receipt for whatever items u buy from pantry car. They r bound for that. than u can proceed for complain and action against pantry car contractor. but my experience is that as soon as u ask for a receipt he might had paid u back what more he had charged.
conclusion :- sometimes Bill, invoice or receipt can buy things cheaper