This is becoming a more regular occurance. Flying is not the same thing as it was 20 years ago. When you booked then, you got pretty much what you 'reserved'. Not so much anymore.
This is the main reason I no longer pay for those extra legroom seats. The regular seats on JB tend to be roomy to begin with. And since I have booked, and paid for, those extra legroom seats, and had my seats changed due to changes in the flight, and didn't get a refund, I refuse to pay addtl for them anymore.
You have to understand....when you book your airfare, you are booking a ride from point A to point B, on a particular day. Yes, you have (in may cases) chosen particular seats and a certain flight. BUT....that is not what the airline promises to give you...they reserve the right to make any changes they want to...as long as they get you to your destination on that day. Yes, most airlines will give you a refund if they change your times by more than 3 hrs or so, but that isn't much help when they make that change a week or two before departure and all other airlines now cost an arm and a leg to book!! So, unless you are able to book another flight, at the same or less costs, you are pretty much stuck with what your airline does.
Is this right??? No, of course it isn't. But it is legal.
So, we book the flights that work the best for us, we choose (and sometimes pay extra) for the seats we want. And the airline is pretty much free to do whatever they want to do. So, just be aware when booking flights...nothing is etched in stone.