Indigo Airlines - Denied Boarding

I would like to share my bitter experience with Indigo airlines and seek your help in this regard

Reference:
Airlines:Indigo
Flight No: *E ***
Origin: Chennai **.**
Destination: Hyderabad **.**
Date of Travel: **th November ****
PNRS:
*. VMZ*TG = Gautam B V and Shamantha K
*. ULV*XG = Jyothishkar Reddy Kasireddy and Indira Reddy
*. RIF*XC = Aneesh B Reddy
There were * passengers, * passenger (Jyothishkar Reddy Kasireddy) was a wheelchair passenger. I (Gautam B V) managed all the checkin bags and advised the other passengers along with the wheel chair passenger to rush to the gate.
The flight departure was at **.**, * passengers out of * were at the gate around **.** but the staff didn’t allow the passengers to board the flight. Hence all * of us were forced to take the next flight **.** hrs by paying the fare difference of **** INR for all the * passengers (**** INR per person).
This was highly disappointing, we requested the airlines many times through email to investigate this and give us the refund of the fare difference paid but they are not ready to do, hence i kindly request you to investigate this issue and arrange for the refund of the amount we paid towards the fare difference from the Indigo airlines.
Note: If the Wheelchair passenger is late then its airline staffs responsibility.
Regards
Gautam