gst refund

Sir Plz reply ..its urgent querry.... Our company is covered under inverted duty structure i.e input is taxable at higher rate than output. We export our product approx 30% of total sales on payment of igst n take refund of this igst. But when we apply for refund of balance credit accumulated in for inverted reasn deppt has rejected our application stating d reasn that if refund cannot be granted for inverted duty if your export is subject to export duty... Plz tell whether thid reasn is valid... Because if this is the case credit will always flow in our acc due to inverted reazn n we will not be able to claim refund of 70 % portion applicable for domestic sale