Air India — issue of no seat availability certificate

Dear sir/ madam,
I had a booking from chennai to srinagar on ai440 & ai825 (Airline booking reference hmcp7) on 19 feb. As ai 440 was delayed for 3 hrs 24 mins i reached delhi late and was not able to catch ai 825 to srinagar as the flight had already left. Refund was processed for ai825 as there was no other air india flights available on same day anf flights on next day 20 feb were available but no seats were available. So i had to travel by goair.
For the purpose of reimbursement/ claim my cda is requiring a no seat availability certificate for 20 feb 18. You are requested to provide the same through email/ post
I am maj santhosh mohan doss
My address is
632 sata bty
C/o 56 apo
Pin 926632