Ripped of and don't care attitude

Every time I order an streetwise one at the Brentwood park KFC I get given a small mash and gravy when I ask about it I get told that it is on promotion that's why I can only get a small we are getting ********** the promotion states and I quote (1 Piece of chicken cooked to golden perfection, a warm mini loaf and large mash & delicious gravy.) At this branch I also have to basically go back every time to get s****s, ketchup etc. The staff is rude if complained to both the managers already and just get a don't care attitude.