Indigo Airlines - Paid Extra Charges after Issuing Boarding Pass

I was travelling from Delhi to Chennai with * more Relatives, Dated *-Aug-**** Flight (*E-****) Dispatch time was *:** AM, and we reached Airport by **:** PM (*-AUG-****). We took the Boarding Pass at *:** AM (*-AUG-****) & we sat near to gate no ** (Terminal * New Delhi Airport), as gate no ** was mentioned on our boarding Passes. At *:** we heard the announcement for our flight & it was the only first & last announcement for *E-**** flight, By *:** we reached to gate no ** & one guy from indigo told, Your flight got closed, now you have to take next flight by Paying **** INR/ Passenger Extra, I asked him, how it’s Possible Because After the Announcement, We took only * minutes to reach here, Then he told this is a silent airport they do like this only but where as they were doing the announcement for other flights which were going to Bangalore, Patna, Hyderabad more then * - * Times, Even they were calling by Passenger Name, Because after Boarding Pass Issues They call by announcing Passenger name. But For flight (*E-****), they did the announcement only once that to ** minutes before the flight dispatch Time. Even they dint call our name at last & first Announcement. I feel Their Intention was to miss the flight by few passenger which they can accommodate in next flight & they can earn money.
Then After lot discussion with Indigo Employees I paid **** Rupees & got new Boarding Passes for Next Flight.
Who is Culprit for this Incident - Flight Announcer, *st Reason - Because Once the passenger has Boarding Pass they can call by the Name also but He has not done for this flight & he was calling by name for others Flight Passenger,
*nd Reason- He has done the announcement once that to just ** min before the flight dispatch time.

My Analysis Why Indigo is doing this Fraud - Announcer was knowing that in next flight few seats are available & If he will do announcement late so he will Move those passenger to next flight, & Airlines will get Profit & He will get some Rewards.
This Incident is not happened first time, after discussing various frequent flyer they told same this happened with them as well.
I want Indigo should stopped this Fraud thing to make money and Refund my **** Rupees.