I think you got a raw deal. This should have been rectified before departure and you should have been offered to keep all compensation and offered different flight of the neext day's with a hotel room.

If a person can not sit in a seat with the arm rest down they should be charged for more than one seat.

FA's should never demand that you be more accomadating than other passengers. In this case, they were asking you to more that the other passenger. Sure they can ask for favors and you can respond as you see fit.

You should write and call until you get someone who gives d@#n. You were offered an arrangement based on the information available at the time ( a full row of seats in coach). If that information changes so does the deal.

I am sure you wouldn't have complained if two normal size people took the seats.

I bet that they have had complaints from overweight people in the past who have felt discrinated against or other things so are on extra laret to be accomadating. That;s fine all should be treated equally and fairly and that includes you.

I would demanded thye take me off the flight.