If the ticket was paid for with a Plastic Card, the refund is made to the same plastic card.
If the ticket is issued at the Smart Light or Smart fare and you have chosen a voluntary refund, then in accordance with the fare rules, the funds are not refundable. You can exchange your ticket (provided that the Smart Light fare is booked before the flight departure) through the airline's call center. Additional fees may apply.
You can read more about the return policy at the link