Refund of sad - customs to manufacture exempted from excise

Dear Sir,

We are having a manufacturing  unit in Haridwar. the unit is exempted from payment of excise duty under notification number 49/2003 & 50/2003. As per existing cenvat rules we are not entitled for credit of CANVAT. our unit is exempted from payment of excise only not from payment of VAT. we are paying VAT and credit of same is not taken by end customer. 

We are paying SAD- Customs. Now my query is that becasue SAD is imposed as compensatory duty in lieu of Sales tax why   we are not allowed for taking refund for SAD/ whether we are allowed to take refund of SAD

regards

anant