Is gst applicable on refund of returned goods

Hello

I reside in Mumbai, Maharashtra, India.
On 30 October 2017, I purcased an Philips remote control for Rs 1600 from a Philips
authorised service centre and got a recipt for the same.
However I returned it the very next day on 31 October 2017 and asked for a refund.
The shop manager insists on deducting 28 % GST on Rs 1600 and is willing to refund
only Rs 1151.
The remote control was manufactured in 2010.
Please suggest if the action of the shop manager is justified and what should I do.

regards,