store brand long life milk

This is totally unacceptable. At the end of May I bought 2 6 packs of long life milk ( house/store brand). I finished the first 6 pack, today I opened a third carton of sealed milk, as I'm pouring it into my tea I see a black ball, when I take it out of the cup with a s**** I realise its a fly!! How disgusting is that...I vomited in my mouth!! I'm a regular shopper at Checkers and this is the first time I am faced with this problem. I am highly disgusted...how can I be sure all the other goods are safe? How do I purchase milk again without screening each use? What if I had to finish the carton and only saw the fly with my last use...this could have caused us serious health issues!! I have 2 girls that love milk for goodness sake!