Uk Vistara — vistara cancellation charges on refundable ticket

I had booked a ticket with pnr oi3mu8 which was refundable and i paid 5400 rupees. When i called them to cancel they advised that i'll only get 600 rupees back. This is really insane. I had cancelled tickets in the past from another airlines as well and they only deducted around 2500 rupees. I'm expecting at least 2500 rupees to be refunded.
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