Sour Danone Yogurt

We buy a few six packs of Danone Yogurt for our two boys every month. They love to snack on the Yogurt normally after school. Last week the Yogurt ran out so my wife went up to our local Shoprite to buy a six pack. When she got home my little boy immediately broke one off to snack on. He complained that it tasted sour. I smelled and tasted it, it was off. I checked the expiry date and it was the 20.11.2019. my little son really wanted the Yogurt and started crying so my wife went back up to the shop to change it but they were already closed. We had to wait for the next day to have it changed, to top everything the next day the people at Shoprite were so unfriendly and she had to wait a long time before it was changed. This has been really disappointing for the standards of Danone. If my kids did not like the Yogurt so much I will never buy it again.