Cleartrip — Processing of refund

I have booked flight from Delhi to Jaipur on 13 August and flight was canceled by airline itself.
Air India gave me in writing that full refund has to be given on their own letter head.
It’s being 3 months that I am not able to take my money back when the airline cancelled the flight and they even told on letter head that 100% refund is to be given in this case.
Kindly help me in this case, very very clear case .