Unavailability of proper invoice even after 12 days of complaining

I’ve purchased a HP laptop on 6th october. The invoice that i received with laptop was not having the serial and product number that are required for claiming and extension of the warranty. As a part of the Diwali offer, HP offered me an complete Accidental Damage Protection warranty for next 2 years only at rs.999. So i made request to the Amazon.in customer service representatives to mail me on 14th october. They asked me to wait for 48 hours within which they will mail me. But since 14th I have made 4 complains to them but they have not taken any action. Every time they told that they have informed their billing department. Finally I lost my offer under which I would have saved more than rs.1500.