Does Volaris not fly that route daily? If it's only a couple of days a week and they're moving the days around, that would certainly be a problem. I guess this is a risk you take when booking a LCC.

I would immediately call Volaris (if you don't speak Spanish, it's probably best to find someone who does who can call on your behalf). It might be possible to have them reroute you via a connection in MEX. While not ideal, it could at least ensure you get to your destination and return home on the right days.

If that's not an option (and I have no idea how accommodating Volaris will be; I've only flown them once), you might have to book new flights with another airline. Given the date change, you should be able to cancel for a full refund.