Poor service

Good evening I have bad experience with McDonald's in dobsonville point Soweto, yesterday(6 oct)at around 8pm I bought a happy meal with milkshake and forgot to take the milkshake, tried to call but no answer today(7oct)went to let them know what happened and I still gave them all the information regarding my order and I was told that it's not their problem because it was different staff members. So my question is I paid for something that I didn't get?