Sour yogurt

I have contacted Bosparadys Melkery direct to lidge complaint about low fat 1liter yogurt sour. It was boiling inside. 2nd time yogurt was sour. i Told the lady about it and have proof when bying and opened it. To no avail. Do they care about pensioners keeping on losing money. 1st time bought from PNP and 2Nd time bought from President Hyper. Both times it was horrible.