safari rotten beetroot salad

I buy my grocery at Checkers Mall of Africa monthly, but this time around not sure l can trust the food they sell. On the 3 April 2018, On my grocery list was 2 Safari Sweet&Sour beetroot salad. The 1st one l used was fine, it tasted the usual. But today when l opened the 2nd one for dinner, it really tasted funny (like it is rotten) the smell was sour, funny because when l dished up, couldn't notice the smell until l had one or two s****s in my mouth. At first I couldn't tell whether was the food or the salad till l tasted only the salad, coz my food was fine. I looked at the expiring date and it is: 26/10/2018. Wasn't sure whether I should go to the store and complain, but because l do not have the receipt to prove l bought the salads from the Checkers store in Mall of Africa, l couldn't. If anything happen to me, pls note l already told my family to sue the store...And l have talked to few friends about this incase they buy the salad to be aware.