Vistara — rescheduling vistara flight without any intimation

My flight was confirmed and booked for 26th sep in uk705 which was a direct flight from delhi to kolkata at 7:30 am. Suddenly i got message from vistara that the flight has been rescheduled and now will go via bhabuneshwar and reach kolkata at 16:35. I have my onward journey booked in the afternoon which i have to cancel and there will be no refund for that.

This is the message i got from ms. Komal from customer service:
Dear mr. Saurabh, thank you for your time and speaking with us. Sorry to disappoint you. We understand delays are frustrating. The flight has stopover at bbi for refueling. Appreciate your kind understanding. Thanks. Komal.

Do you really think this is an explanation?
Need proper assistance or i have to go to consumer court.