This is a strange switch if there was not a change of aircraft. It is especially strange because you were in exit row, so this could not be a change to accommodate a person with a disability, nor could this be a change to accommodate parents sitting together with young children. If I were you I would call in, ask to speak with a supervisor, and push this a little further. The GA in AMS will almost certainly not see the note that the agent put in their without you calling attention to it, and I would not expect the KLM staff to be helpful with this issue at all. In other words, try to deal with this before you get to the airport.