Cheated of Chicken at KFC

I bought a Streetwise three this weekend on Saturday at the Drive through in Hammanskraal, Pretoria .They cheated me of my Chicken instead of two three pieces which I should get they gave me two pieces.I only realised this way later when I was already far off.This is Unacceptable and it's not first time KFC employees have cheated one of Chicken, sometimes I have to check to make sure all pieces are there otherwise it has happened before but luckily I have checked, then gone back and they rectify the situation but I do not understand why it happens in first place as order is always very clear.I see a bad trend here which must be stopped.