(3)Where a refund is due to the assessee in pursuance of an order referred to in subsection (1) and the Assessing Officer does not grant the refund within a period of six months from the date of such order, the Central Government shall pay to the assessee simple interest at fifteen per cent. per annum on the amount of refund due from the date immediately following the expiry of the period of six months aforesaid to the date on which the refund is granted.