Jet Airways — jet airways flight from chennai to pune cancelled

Address:

Chennai, Tamil Nadu, 600061

Firstly, i booked a flight for apr 7th 2019 to travel along with my parents who are aged over 70 and this flight was scheduled to depart at 10:25am and arrive pune by 12:15pm

Secondly, got 2 to 3 notification regarding change in scheduled.
1. From 1 stop flight, it changed to 2 stops (Maa to bom and bom to pnq)
2. The departure timing was changed to 7am which is extremely challenging for aged passengers.

Now all of a sudden, i receive a notification on 18th march that maa to bom flight is cancelled. I am neither able to contact customer service as it take more than 30 mins, i don't know about the refund status, alternate flight details etc. How can i claim refund of a flight that is cancelled by airline?