Air India — misrepresentation of facts and wrong info to customer

Address:

Mumbai City, Maharashtra

I booked a ticket for 9th dec with air india for mumbai to india which i wanted to reschedule for 10 feb we called air india on 5 dec at 23:20 hours, their official informed that ticket can be cancelled or rescheduled before 24 hours. My pnr no. Is he7jt
Wen we called again for rescheduling a day prior on 7th dec around 23 hours, another official confirmed.. It cannot be done as 72 hours already gone and he told he will ask concerned team to call back on 8 the morning between 7 to 8 am and no call received from them.
Now we are following up with them but they have a standard reply that they can't do it. They are not taking the responsibility of words of their official even.