HappyEasyGo — Purchased Free Reschedule Flight Ticket but while rescheduling it is charged

Address:

Plot no. 242 & 243, Phase IV, Gurugram, Haryana 122015, India

I have booked flight ticket from Jabalpur to Hyderabad for 10th April with Reschedule option and paid an extra amount while booking the ticket.
Now when I want to reschedule the flight the HappyeasyGo is charging 1555rs as a fare difference when the fare is the same for 3rd April and 10th April and HappyEasyGo is charging 300rs service Fee which is not applicable when I have already paid that amount while my initial flight booking.
I have attached the screenshots of the fare cost for 3rd april and 10th april which is the same none other than in HappyeasyGo website.
I have also attached the Ticket and Free rescheduling rule screenshot of the company.

Name :- Kolipundu Pranay
Order ID :[protected]
Flight SG - 3748 JLR → HYD

Regards,
Pranay
+91-[protected]