Milk goes off within one day of opening

I recently purchased two cartons of the Spar Extended Shelf Life Full Cream 2lt from Spar in Craighall park. Both Cartons had an expiry date of 13/1/2015. Both of these cartons were stored in my fridge until I wanted to use them.<br> <br> I opened the first one on the evening of 20 Dec 2015 and it the milk was fine, when I wanted to use it the next morning, the milk had gone sour. I then opened the second carton to use. This milk was also already soured.<br> <br> This product should not be advertised as having a 35 day shelf life if both can go sour in such a short period, despite being stored correctly, a week after being purchased.<br> <br> I no longer have the batch numbers as both cartons have been thrown away.