You have up to 45 days to file an Item Not Received dispute.
First, as pierrelebel suggests contact the seller and ask for the shipping date, shipping service and Delivery Confirmation number. Now. The seller should be able to provide the first two, but the DC number would be expensive (if you did not pay your US seller $20 or more for shipping, there won't be any tracking.) Don't worry about this, asking is mostly to get a reply.
If the reply is unsatisfactory, then you should file the INR dispute. Do this 30 to 40 days after payment, and don't wait til the last day. The clock clicks down to the last second.
When a Dispute is opened, the seller can refund you, ask you to wait a few more days, or give the tracking number. The deadline of 45 days has been extended by the Dispute, so you don't have to worry about that.
If the seller can't provide the DC number, ask for your refund. Do NOT accept a promise of a replacement, not only is it equally likely to "get lost in the mail" but the shipping time is too slow.
If the refund is given and then the parcel arrives, you can refund the refund through Paypal's "send money" service. You cannot ethically have both the money and the product.
