Rotten milk

I bought a 2 litre of milk at one of your stores before Christmas. I had to use the milk to prepare lunch that weekend since I had guests coming over. I used it once and kept it in the fridge. On the third day the milk was rotten/spoilt. I was so sad and disappointed because I had to prepare custard for my guests. Why are you as a company taking us for a ride and selling us rotten groceries?