Reschedule interview denied?

I just called USCIS to reschedule my interview appt and the lady asked for the reason (I will be traveling out of state for two weeks to visit my sister who’s having a baby). The lady told me that it does not fall under the approved categories for a reschedule and I have no other option. However, I looked it up online that non-refundable travel is a valid reason? My interview date falls right in between those two weeks so it’s not like I can refund/change one of my flights. Should I call again and retry? I assume I’ll have to provide proof like my flight confirmation and everything. Will it work? Any other options? I’d be really sad if I can’t be there.