Billed for wrong order.Very much disappointed

Im so disappointed that u hand out peoples orders without checking if they are correct.I bought street wise 5,Twitter and 4 Zinger wings at KFC Market street east London.On my way home I decided to eat the chips and noticed that they gave me 2 small chips instead of large chips but I then thot argh!! Myb they made a mistake,When I get home only to find out that I was given 4 pices and I could not go back as I have already eaten the chips but I payed for street wise 5.Im very much disappointed as this is not the first time getting wrong orders.I have taken pictures as proof