Gst rate change in SALES RETURN ISSUE

mahendra sahoo (Gst Practicion) (700 Points)

05 January 2018  
Hi,
I have sold material to a unregistered person in month of July, that time the gst rate was 28%, the said person return the same bill same material for the November while the gst rate is 18%, now which gst rate i should take the entry of sales return in Nov?

Please clarify me