do I know you?

Today at the end of the meal the three women I have been serving place their credit cards at the end of the table. I ask them if they need the check split or if they would be paying equally. They ask for the check to be split. When I come back with three separate bills and place them on the table they look at me like an idiot because their cards are still sitting in the pile. Taking the non verbal cue I ask who is who and they start spouting off their orders. "I had the chicken, I had the burger" and so on. Now frustrated because I was there and served them the food. I do not need to be reminded what they ate. I then have to explain to them I do not know which credit card belongs to which person.