Sastiticket.com — refund

Website:

www.sastiticket.com & skyscanner.com

I looked for a fare on Skyscanner for Mumbai Goa return. I selected an itinerary and they directed me to sastiticket.com for payment and ticketing. After making the payment sastiticket.com booked only the Mumbai Goa sector, the return was not booked as the fare increased (according to their mail) and they refunded the fare for that portion. The issue I have is they charge convenience fee of ₹400 on return fares and ₹200 on one ways. So the refund should include the convenience fee at least of ₹200 but no, they refuse to return it.
They have caused an inconvenience and as a good responsible company should return the full convenience fee. But their response is convenience fee is not refundable. This is such an unfair business practice and actually a theft and unethical act.