regarding claiming the funds back via credit card: This will help the OP not to pay twice, but in his position I would also be looking for someone to cover the 700 euros difference between the 1600 and 2300 euros. If I was not planning to spend more than 1600 euros, it should not be my problem. So the question is who should compensate him for the extra 700 euros: the agent or the airline? I guess in any case it should be the agent- and they should claim it back from the airline if indeed they issued a valid ticket.