The airlines pushed out departure time of my return non-stop flight by half-hour, and I arrive 1.5 hours later (same origin & destination, both within Mexico). However, with this delay I will be unable to make an international connecting flight.

So I asked them to give me an earlier flight on the same day (I checked, and tickets are easily available). They said I would have to pay the fare difference, which is substantial (almost $400 total for all passengers).

Isn't this a ridiculous ask from the airlines? How can they require me to pay because *they* changed the flight timings? My outbound flight is still 3+ weeks away. I am kept on hold when I call (after 45 minutes I hang up), and they are not co-operative via email. What recourse do I have to get them to offer me the earlier flight time without incurring extra charges? I am also ok if they issue a full refund instead.