Spice Jet Airlines — denial of refund

Dear Sir/Madam,
I have booked ticket from delhi to dehradun with SpiceJet airlines by ease my trip for 20/09/2018 (PNR - YBU16T).
Unfortunately, my ticket for same journey was simultaneously booked by my friend (co traveller) by mistake.(PNR- T6PHPV) on same flight.
Now I have two tickets for me on same flight. As i m travelling on same flight, and the mistake is genuine I requested to cancel my ticket having PNR YBU16T & give me full refund of the flight ticket.
I have written to customer care about this but they simply denied my logical request. I request you to look into this matter.
Thank you
Regards,