SELLING EXPIRED AND ROTTEN MILK

Yesterday I purchased Farmgate long life milk (1 litre×6) at Scottburghs' PnP located on the main Street. We have discovered that the milk is sour and now we are unable to use it as we are afraid the kids might get sick. From here on ,we not sure on how to get a refund or a replacement. What was also concerning ,is that there were other brands of milk which were in the shelves but they are long expired (January) at the store.