Really bad attutide and SERVICE..!!

So the cashier decides to ring up the order with one item short where where clearly stated what we wanted..now they feel that they need to inconvenience us and go around to purchase the one item that they did not ring up..this is the most ridiculous service I ever got from MacDonalds I feel that they need to give me an apology as the manager wants to argue with me that we have to go around making it a inconenience for us the customer to go through the same situation again..the driver behind had yhe same situation where they still gave them a cooldrink short but MacDonalds staff still felt like they are right which was not the case..SO WHAT IS HAPPENING MACD'S..?