Vat on discount/credit note

Hi,

I want to know Karnataka Vat Liabilities in following cases:

Purchases Rs 1,000/-
Vat on Purchases @ 4% Rs 40/-

Trade Discount/Incentive/ Cash Discount/ Volume discount on purchases through separate credit Note Rs 50/-
Not vat Reversal by supplier in credit note

My sale Price Rs 975/-
Output Vat @ 4% Rs 39/-

Whether I can claim the refund of Re 1/-?