Milk turning sour

I had bought 2x 2L Douglasdale Milk from Fourways Hyper in Fourways Mall. The purchase date was 28th Dec 2015, and expiry date was 4th Jan 2016. On 30th December 2015 I poured some milk into a pot to boil it and the milk turned sour. I tried boiling my milk again and saw the milk turning sour again. I tried boiling from the 2nd 2L bottle and saw the milk turning sour again. Then I went on boiling the entire milk which was left in the bottles and saw that everything turned sour. Note that there was 5 more days left for the milk to expire!<br> <br> Not a single drop of milk I was able to consume from those 2x 2 liters I had purchased. I'm very disappointed with Douglasdale/Checkers. Either they put the wrong expiry date or the quality has dropped!!<br> <br> This is not the first time that the milk turned sour. Have experienced it many times in the past but this time it was full 4 liters of milk that got wasted way before the expiry date!