Mince gone bad before reaching it's expiry date.

I bought lean minced beef at Pick 'n Pay Brits on Thursday. The mince had a very disgusting smell while I was cooking it,I initially thought that it's my weird smell sensation but then it got even more disgusting that I even tasted to make sure that it's fine. I was surprised that the beef mince gone bad even before reaching it's expiry date. I threw the mince. I was so disappointed in PnP products that I swore that I'll never buy meat goods at the store. Mind you,I cooked the mince the same day I bought it.