Flat Cooldrinks before bottles are even opened

We recently saw the 1.5litre coke on special at Shoprite my husband and i went in to purchase two cases as well as 6 loose for the month as we drink coke daily and that is the drink of choice at home. We purchase our coke for the month as we see it on special so it does save us from buying them daily. As the days go buy we are drinking the cokes and they were flat and we put it df=down to maybe the kids were not closing the bottle as we get to the second case we realise the bottles do not have gas. We could actually press the bottle before it was even opened. unacceptable for customers who drink so much of coke. We don't have a budget to go and buy another 30 coke so we are now drinking flat coke. we will buy a new lot as those finish. For a company that is so big how does flat soft bottles pass your checks before they go out.