Wolf, Since this is not for monetary profit or gain, they didn’t “cheat” you. But you still have a right to be disappointed, the way one would be if a trip was changed due to weather conditions.
Mentchlichkeit would have dictated them forewarning the mass (even a sign on the door) so that people would be aware of the change in plans (I’m sure they weren’t thinking)- perhaps that would be a more profitable topic of discussion.