That's happened to me with La Campesina brand (el barato sale caro). Now I stick to La Vaquita, Lactis, etc.
Used to buy Rica fresh milk but it was spoiled prior to the sell-by date on more than one occasion.
That's funny, it was happening to me with La Vaquita and on SantiagoDR's recommendation, I have now switched to Parmalat. He's been here many years and never had a problem with this brand. A little more money but better.....I WAS TOLD..
Actually La Vaquita around 34 pesos and Parmalat 44 per unit.