Had the worst experience at Cafe Hawkers in CP today

Had gone out with a couple of friends to CP and we had booked a lunch spot at Cafe Hawkers in CP for 20% off the total bill and paid a cover charge of 600 (which was already way too high for a cafe) which would get adjusted in the bill. Upon reaching the cafe, they made us sit at a corner Booth near the kitchen with no air conditioning. Upon complaining they said that the upper floor is reserved for a workshop at 3pm. So why did they take our booking and cover charge if the slot wasn't available?? In the end they agreed to let us sit upstairs but on the condition that we'll be shifted elsewhere after 3! We decided to go elsewhere and just ordered 3 mocktails and fries, got the discount and went elsewhere. Why do these restaurants put up their slots if they aren't available and no way to refund the cover charge!