MakeMyTrip India — Data change not working even after paying Data change fee

Hello, I have recently booked a flight through mmt, and paid extra to utlize free data change option.
Now when I trying to change the date, I see no flights available, however when directly trying to make the booking, same flight is available on the required date.

This really feels like a scam, where you charge extra for the date change and does not allow to change it.
I also tried to call mmt support, where they say I have to pay around 2800 extra and fare price difference, which is absolutely cheating. The price I paid while booking the actual ticket and the new ate ticket I want to book is only hardly 300-400 rupees difference.

I am not sure if this the app bug or a real scam from mmt, but as a consumer I am really annoyed and cheated