Indigo Airlines — Refund of Flight cancellation due to wrong sir name mentioned

I've booked a flight from Delhi to deogarh for 11th December 2025 on which I've by mistake mention wrong sir name and after that I've tried to change that sir name through their customer care and called them multiple times but they always mentioned more than 5 days passed we can't do anything due to our policy, I understand that you policy is like that but I've booked a flight in Oct'25 for flight in Dec'25 2 months back and it's is small mistake and all I'm asking to change sir name from Bansal to kumar and this could happen to anyone but they said you've to cancel to ticket and rebook the same and When I'm doing that I'm seeing out of total ticket fare INR 5256 Refund is only 450 how this is fair, I've only asked them to provide me some flight voucher if you can not provide my more refund but they did not say anything.
My Trip PNR Number is Z9TU5A.
My only request is that If you are not able to make correction and I've to cancel the booking then least you can do is to provide my a voucher for 1 free booking or voucher for 90% of flight value. I'll really appreciate If you can do that.
I'm working in audit department and I'm a frequent flyer for audit assignments and most of the time I'm using Indigo flights and I don't want to change this relationship, Please provide my some solution regarding that.