Make My trip Amritsar - Overpricing and misleading information

I booked my round trip tickets for me and my daughter (* years old) from Make My Trip store in Amritsar. The agents there told me that the tickets are refundable and everything is perfect. Later i asked them to reschedule my return tickets as i decided to extend my stay. They said they'll charge me around **,*** just to extend it. They said there are penalties and i have to pay fair difference. I was shocked as there were no mention of penalties at all when i first booked my tickets. So i asked for a refund hoping it would be a better option. The company said i will only get like **-** thousand as i have already flown one way. But what does not make sense to me is i paid ****** in total and even when i have traveled one way at least i should get half of my refund or just * lakh back. There were no mention of penalties. When i had asked them is it refundable, they said yes it is. I tried talking them through it, the agents there are horrible. They did not provided proper information on any charges at all. I called air india airline, they said they can't help me out, i have to talk with agent only. All this is exhausting and i'm losing a lot of my money just because of their misleading information they gave me.