Air india - Refund not provided for cancelled flight

My parents were to take a SFO-BOM flight with Air India which got cancelled, and have not received refunds worth *,**,*** as was promised
*) My parents, with medical issues, were kept boarded for * hours on a flight, and deboarded in the middle of night in a foreign country without any accomodation or any rebooking
*) Instead of rebooking the flight, we were promised compensation (both written and orally from Mr. Manoj Gupta-Duty Manager (SF)) for the new flight. Instead what we get is a measly **,*** refund for * SFO-BOM tickets.
*) For * months, we do not get any response or are told what we should do.
*) Emails received from Air India promised a refund and asked for bank details after we claimed the *,**,***; however, we didn't receive any money, leaving us in limbo.
*) The new flight was significantly more expensive. While I received a refund for the old flight, I'm still awaiting the promised fare difference according to the letter attached.