Air India — preponed departure of flight without intimation

Address:

Sector 6, IMT Manesar, Gurgaon, Haryana, 122050

This is regarding my recent booked air ticket to Kochi from Delhi on 20 November 2019 on flight AI 933 which was scheduled to depart at 0600 hrs.
I reached Delhi airport T3 at 0430 hrs, waited at the queue, and while at the check in counter at 0500 hrs, to my surprise, the person tells me that the flight boarding time is over since flight is leaving at 0510 hrs. (refer attached screenshot also)

There was no prior intimation given to me or my travel agent on mobile/email regrading this change of schedule and because of which I had to miss a very important meeting with my client. There were few other passengers also with me who never got such a message and eventually missed the flight. I am filing this complaint to understand why such an important information was not passed on timely and demand a thorough probe on this matter so that this is never repeated in future.