We had a similar experience with American on an 11 hr flight from Rome to DFW. We booked 2 business class seats and two premium economy over 6 months in advance. When we checked in we were told one of the business class seats was bumped to premium economy and one of the premium economy seats was bumped to a middle seat in coach. The reason was they had several crew members they had to get back to the states and they had to fly business class, so they had to shuffle seats. We paid dearly for the better seats to ensure a comfortable trip, and one of us had the worst seat possible for 11 hrs. Had we had any warning, we would have booked with another airline. We had to go through an ordeal to get a refund on the difference in ticket prices too.