Deneys Swiss Milkshakes

I recently purchased 2 Deneys Swiss Dairy Milkshakes ( Bubblegum and Chocolate) from the Checkers at Rivonia Village, Sandton. When I opened the milkshakes, the contents were sour, thick and slimy. Definitely not consumable. I don’t know what the cause of this could be because the expiry date of the milkshakes is 23/11/18 and I purchased the milkshakes on 12/11/18. I often buy the milkshakes but I’ve never experienced something like this before. I’m really disappointed.