If you search INR, you will find so many threads about this situation.
Here is the famous Shanti letter to be sent to the buyer:
I am so very sorry to hear that you did not receive your package. If we are unable to find it I will, of course, issue a refund. I would like to try a few things that have successfully located packages in the past. I will call your post office and initiate a trace on the package. Sometimes the package is simply there, awaiting pickup. I will ask to speak with your post master who will check with your carrier. It may take a few days for the post master to investigate the package.
Please, do, ask your family and neighbors. Many a lost package was simply laid aside by a family member and then forgotten. And sometimes your postal carrier leaves it with a neighbor because s/he doesn’t want to leave it out in the weather.
If these measures don’t work I will file a case with the postal inspector’s office. Many carriers now have scanners that are equipped with GPS tracking and the postal inspectors can find out exactly where the package was delivered. If your package was delivered to the wrong address they may be able to retrieve it and get it to you.
I will let you know what I find out and, please, let me know if you are able to find it yourself. If we can’t find it within a few days, I will refund and let you know what the postal inspectors find out. Be well.