Rang Mahal Authentic Indian Cuisine (已結業)

It said it should have 20% off if I book through open rice online, but when I pay the waiter said it's not included in lunch buffet, and the reason is the lunch buffet is already very cheap. I don't know why it didn't mention in open rice app and no one was telling me abt this after I make the reservation or step in the restaurant. Food is ok. But if I know there is no discount I would just pick food from menu instead of doing the lunch buffet. Can anyone explain why it's not included for lunch