Goibibo.com - No Rescheduling for an international flight that was rescedulable

Hi
I had booked a round trip flight for my wife from Mauritius to Bangalore and she flew to Mauritius in May ****, the return flight was in late August and I had booked a ticket that had option to reschedule and cancel. But, now when I am trying to change the return flight date, they are saying it can't be done. I have called and talked to various customer service agents in last * days and each single one of these liars have promised to give a call back but none of them did. I dropped emails also but no one replied. There is an option to write to management on their website but need to wait for ** hours for ticket to get resolved and it has been more than *** hours and still I cannot write to management. I was a loyal user of Goibibo and my friends too. They have not only lost customers like myself but they have broken the trust as a brand. Hope someone helps me get my flight rescheduled