unprofessional manager

My cousin bought milk for her infant (S26)on the 27 September at Pick n pay Wonder park .only to find out that the milk has expired in May already .when we return the Milk to complaint that they have sold us and expired Milk, we got the Manager Billy of which i think he handled the matter unprofessional .he was telling us the issue is with the supplier by supplying them the expired goods ,is it not the shop responsibility to supply us with Fresh Goods ?,we already Fed the baby and if it happens that she gets sick from that milk ,who is responsibility it is ,please look into the situation and get back to us on ********** 956