Purchase returned of excisable goods.

Dear All, My Query is as follows:- I Have Purchase Excisable Goods in April and Taken credit against the Invoice in Aptil. Now I have Returned the Goods Purchased From April. I Have Raised Debit Note As per Rule 11 In Tax Invoice Format. Question 1: What is the Effect Of Excise Duty In Modvat Account? Question 2: Whether I have to pay the duty or not? Question 3: Can Seller Takes the Credit or not?