HappyEasyGo.com/ — fake 'zero rescheduling fees' option

Website:

www.happyeasygo.com

I booked a flight ticket from Happyeasygo.com for travel from Pune to Chandigarh. I had chosen the option of 'Zero Rescheduling Fees' which states that I can reschedule the flight ticket any number of time with 'ZERO AIRLINE RESCHEDULING FEES" and need to pay only the fare difference and HappyEasyGo fees of Rs. 300.

Now that I want to change the date of travel, the customer care is demanding Rs 2900 extra which one of their executive say is the Fare difference and the other say it is Airline Penalty.

I have talked with the Team Indigo as well and they confirmed that there is no price difference of the flight.
Team at happyeasygo is demanding extra money for rescheduling.
This is a clear case of Cheating and Fraud.

I have already shared all the required screenshots to the customer care via email and they are giving vague reasons and demanding extra money.