Yes this sucks ! And the government allows this only with airlines ? Maybe lol! Let's say it was Holden that rang you and said look we can't give you a six cylinder car in blue paint as we are not going to produce that colour any more but we will have your car ready a day early but in yellow ,sorry about that!
Would you be able to cancel the purchase ? I would think so ! But the airline ,because of the way the rules were written , is allowed to tell you that you purchase only buys you a seat on a plane ! Not the one you picked ! Not on the plane they said they were going to use and not on the say you want !