Seems odd to me the dealer are saying its because of a moneyshift and then say you should have changed the chain at 75k. Either it's because of mis-shift or the chain failed in some way, or what are they trying to get too.
Vita, can you remember at all if you mis-shifted at any point? It would be quite obvious as the car would rev into oblivion, its quite easy to knock into 2nd instead of 4th when changing really really quick, although very rarely would someone do that!
But it looks you might have to cut your losses, but you shouldn't loose a huge amount of money, these are popular in demand car, and someone out there wouldn't mind buying a car 1k under the normal price and just do an engine swap or repair.