PICK AND PAY GREENSTONE FOOD POISONING CAUSED BY EXPIRED MILK

On Monday evening I purchased a few groceries at the pick and pay hyper in Greenstone, Edenvale , to my surprise one of the items was 1 litre of Douglasdale Full cream milk had in fact expired . I got a call from my sons school informing me that he had been taken to the sick room @ school after he complained of dizziness , stomach cramps and a slight fever ,to my surprise one of the items was 1 litre of Douglasdale Full cream milk had in fact expired . I used it in the morning to make both him and my elderly mother cereal .

I tried contacting the store with no luck , the phone number provided on the till slip just rang no answer over3 times .

Now I want to know what I should do because this is a serious case of food poisoning , Pick and Pay I need answers please