EaseMyTrip.com — Convenience fee charged even for rescheduled flights

I have booked flight tickets for GoFirst airlines through easemytrip.com. The ticket was of flexi type which means I can reschedule flight tickets without any extra payment apart from fare difference.
I have rescheduled the tickets couple of time because of pandemic. What I have noticed is easemytrip is charging convenience fee for everytime I reschedule my flight tickets and they are not even refunding back my previous convenience fee charged. So every time flight is rescheduled extra convenience fee is charged but old one is not refunded back. No where in the ticket they have mentioned about these hidden charges. In the ticket they mentioned only about cancellation charges. No reschedule charges. When I asked them there is no response from them. Its been more than 1 month I am waiting for the response.
request to kindly take an action against them to restore the transparency in the flight tickets
Attaching one of the ticket for your reference