Accounting and IGST for Sales Return of Export Sales

I had exported goods worth 1,00,000 and paid GST @5% = Rs.5000, while despatching the goods. Normally, Govt refunds the Rs.5000 to our Bank Account after the Shipping bill is raised.

My Query is the above goods got returned to me due to a technical reason. I have raised a credit note to my customer, and hence the sale value gets knocked off in the nett sales. Now, should i pay the Rs.5000/- to the department?.IF yes, should i pay now or only after i receive the same in my bank?. Where should i mention this in the GSTR Forms,?. Please help