Pick 'n Pay for your food poison

These shops pick product items markdown the price and put them all together this seems great for consumers... Except these products are about to expire or have already gone off! I bought a dairy drink Friday evening and when I got home I opened it and it was rotten it smelt vile the very next morning I tried to return it and was told because of the "marked down" sticker its non returnable. Nowhere on the product or the receipt is this communicated and it's impossible for it to go off in the 15minutes it took for me to get home so Pick n Pay is selling expired rotten products instead of this stuff being disposed off.