Jet Airways India - Air ticket charges not refunded

My parents had booked tickets from new delhi to london via jet airways for **th september ****. they had a valid UK visa from ** september ****. they were not allowed to check in and board the flight. when they asked for exchange tickets for the next day they were asked double the price. then they declined and the personnel attending them told hat **** inr will be refunded each. but after few hours jet airways personnel refused and called it a no show ticket and said they will refund only *** inr per ticket. what a joke. i have contacted even their appellate authority and its been one month and i am still awaiting their reply. I have advised my relatives and friends to not use jet airways because of their poor customer service.