I sent a rented textbook that I bought through amazon's rental service back 10 days before it was due. I did everything the instructions told me to do. I taped the address to the outside of the box, double checked it, then dropped it off at the post office through the do it yourself line. It did not require a stamp or anything. It has been 12 days. The package cannot be tracked AT ALL. I've put in the tracking number many times but it keeps on saying that the number cannot be found. I even went to the post office and she told me there was nothing they could do and to just call the automated support line. The number was no help whatsoever because it kept on trying to track a package that could not be found. I called customer service to talk to an actual person. They got rid of my late fee charge which gives me 15 more days, but if the package isn't found before then, then they will charge me $200. I don't know what to do! I've filed numerous complaints online, but received no answer. I'm so upset. Does anybody have a suggestion?