Indigo Airlines - Not allowed to board the flight inspite of reaching gate 15mins prior departure and check-in 3hrs be

We checked in * hrs before the flight departure and we reached the gate ** mins prior to the flight departure and we were not allowed to board the flight. Our check in baggage was offloaded without any notice. The airline argued that they close the gate ** mins prior departure whereas this is not followed sacrosanct for all indigo flights across all airports. The previous flight which we boarded allowed boarding as less as * mins before flight time