3-4 flakes x2 per day is a pretty decent amount of hay. Even in the winter, our guys only get 2 flakes x 2 per day plus their grain.
What does your actual contract say with respect to the quantity of hay, grain and turnout. I can imagine if it says unlimited that you might have reason to be irritated, but I suspect that it states certain quantities and then you would have a right to request that quantity.
I *personally* would never board at a facility that only fed 2 flakes 2x per day in winter unless I owned an airfern QH. Many, many horses would NEVER stay a healthy weight with that little amount of hay unless the flakes were from 70lb wire tied bales or they are getting fed an unhealthy amount of grain to supplement the lack of hay intake.
Most of the barns in my area don't specify exactly how much hay is fed per horse because it will vary. Easy keepers will not need as much as your average TB.
Most barns around here either specify free choice, unlimited OR how many hay feedings they offer per day. I've never heard of anyone actually stating they feed 2,4 or 10 flakes a day. If they did I'd be concerned because I dont' subscribe to one size fits all horsemanship
I'd be extremely mad if they made such a drastic change in my horse's diet without first consenting with me!
To my knowledge it's always been customary and professional for BO's to notify the boarders to any change in the service. If the OP had to pay extra for hay in the summer then she should have been notified ASAP, preferably right as the new BO's took over.