Does sound like your fridge is set too warm Fatboy tbh, I've never seen milk go sour within at least the first 4-5 days from any source. I'm sure the odd bottle does get left out, but it would be incredibly rare. Most people tend to get smaller bottles of milk more often rather than bigger bottles, so its just more likely your delivered milk isn't kept cold enough, but you use it within a day or two rather than a 2-6pint carton you'd get from the supermarket which in a not cold enough fridge would go off before you could finish it.
Also, did the OP say he has 8 weetabix every morning? I find that more shocking that 28pints of milk a week tbh. Unless you're a professional athlete burning off a few thousand extra calories more than most people thats an insanely large breakfast meal.