MakeMyTrip India — Website is not letting me changes dates.

I have booked a flight from Delhi to Heathrow. I have to extend my trip and postpone my ticket. Once I am trying to change my dates the app take to a change with say the following: Online Date Change not supported.

I have put in a request with app to arrange for a call with an executive, but no reply up till now it’s been 8 hrs and my flight is in 2 days. I tried calling all their numbers but no luck what so ever.