The problem I have is that, even if I were prepared to accept 75% of the price of the leg rather than the whole ticket, I do not know the cost of the individual legs (it was an open-jaw, returning from Seattle). So I have no idea whether what they have offered is appropriate.

Are there any successful experiences of people getting 75% of the ticket rather than just the leg? If so, how best to pursue -- another letter? Legal action?

Thanks again for the help.