MakeMyTrip — Causing hassles to customer due to the fault of their employee

Address:

Mumbai Suburban, Maharashtra

I made a booking with makemytrip.com for a british airways ticket from mumbai to phoenix via london and chicago on 23rd june2012. I later rescheduled my london-chicago flight for an earlier flight on the same day since I had to travel with my colleagues and I had not got the same flight as them i.e. BA 295 when I booked initially.I called make my trip many times to check for availability in ba295,and on 17th july 2012 ,their employee told me there was 1 seat available and I would have to pay 5900 inr extra to get a seat in my desired flight(4000-charges of british airways for date change+500-charges of makemytrip+1400-price difference in the previous ticket and the one I wanted)and I paid extra 5900inr to get my desired flight from london to chicago.But I kept calling them daily ever since, since the correct ticket was not available on my account in make my trip and they told it is a technical error.Now they are telling me that the employee who made the change in my itinerary made a mistake in pricing the ticket due to which I am not getting the correct ticket although the itinerary on check my trip and ba.Com is correct and they are requesting me to give another option whch is absolutely impossible for me.I have paid to have the following schedule along with my colleagues: mum-lon - 2nd aug - ba138 lon-chi - 2nd aug -ba295 chi-phx - 2nd aug - ba5780 as I am travelling with my colleagues and I cannot travel on any other date since I have already arranged for my accomodation in phoenix from 2nd august 2012.
They have not given me any assurance and say that either there will be a difference of 50000INR to get the desired schedule or they will give me my original schedule which I had booked the first time.But it is unfair to me to suffer for their mistake.They have told they will call me back and I am waiting for their call currently.What should I do now?