sour milk

I did my monthly grocery shopping at lemon tree pick n pay, purchased milk it expires the 1/09/17 by yesterday it was already sour 28/08 so I work at mall of the south went there to take it back to get told they a corporate pick n pay not a family pick n pay and can't help me with such an arrogant attitude from a manager. This is not the first time the milk goes sour days before d day, so I ask to speak to another manager , she then proceeds to speak Zulu to him and tells me he says I must tell you the same thing, bad altitude and shocking customer service