Mcdonald's Restaurant

Very poor customer service - I order a chicken sandwich with combo (which includes a medium drink and a medium fries) and asked the drink and fries to be down sized since I did not want to waste food. The person at the counter and the manager say: "We don't have that in the menu and your only option is to get the sandwich, drink and fries separately which adds up to be more than the price of the combo"

I still can't get my head around the fact as to why on earth a person can't give me small drink/fries even if I'm willing to pay the price of medium drink/price. Please save me from these dumb people!!