Serving Notice Period

I work in an NEET coaching Institute and it's been 7 months. My dad is having serious health issue and am a single child and am supposed to be with him. So I planned to resign and forwarded a mail intimating the same. Since I will have to bystand with him in the hospital i can't serve the notice period of 45 days. But the management is not agreeing with that and they don't give the acceptance of resignation till now. And verbally told me that am on notice supposed not to take any extra leave even on the funeral of my aunt and even said the won't do any final settlement unless I come the day of my aunt's funeral . When in the same day my dad was hospitalized. I really regret working in such an unsupportive institution. I have received offer letter and appointment letter after 6 months of joining. In that 3 months was probation period. I literally can't serve complete notice period and they didnt formally accept my resignation. In this situation, do I really need to serve notice period and do the institution have the right to hold my relieving letter and experience letter? What am I supposed to do?