Non shipment of on-line order

Bunchesofbooks.com claims they shipped my textbook on August 29. Their email said to expect the book within 4-10 days. Yet, they provided a tracking number that USPS doesn't recognize. I have emailed them 4 times since September 2 and they are ignoring my emails. Yet their web page says that they respond within 1-3 business days.

Since then the USPS website has acknowledged that they have received an on-line notice from bunches of books of an "intention" to ship a book.