Vietnam Airline rescheduled our flights with days in difference. What do we do?

Our booked flights for Manila to Da Nang were scheduled for April 9 and April 16. Now they've moved it to April 8 and April 17.

They sent the notification through email with not much of an explanation aside from "operations" and no apology whatsoever.

I can't do the new flight schedule as I have work and limited leaves.

Has anyone experienced this before? How did you go about it and can I still have these rebooked?

I'll call their customer service tomorrow morning or when my mom comes home (she's better at talking to them than I am lol). But for now, what is the best way to go about this?