Coffee and chips served after 40 minutes

my child ordered coffee and chips at McDonalds and had to wait 35 minutes whilst they were serving other customers,ignoring her,she is 17 years old but small built.I had to come out if the car to find out ,they made me wait another 5 minutes,when I asked for a Supervisor on duty,the lady at the till just ignored me and continued working,I then asked the other one on the floor to call the Supervisor.When they finally helped us I asked for a slip as I needed it as proof of the time when the order was placed and she told that she does not have it .I then insisted on it<br> The Supervisor just said,sorry.This is not the first time that a child receives this kind of bad service at this branch of McDonalds and the owners must address it.