Expired cake made my child sick .

I went to PnP woodmead to buy a cake on Sunday 14.35. I've spent R392.59 the cake was R90 I bought the cake because it's a chocolate flavour and the expiry date is on Saturday 25 May .Only to find out that the cake expired and made my child sick ,the taste or flavour for chocolate is not there and it really expired,I am in Belabela I only go to Gauteng on weekends ,Iam really disappointed so basically it seems like they changed the dates knowing the cake is old .