Chegg Returned a text for buyback, got no check in return Internet

Chegg offers to buy back college textbooks.  They set a price for the buyback and if you accept the amount, then you send the book in to Chegg.  In return, they mail you a check for the designated amount.

I did this with the textbook Porth's Pathophysiology.  I followed all of the instructions, but never received the check.  After emailing Chegg, I received an email back from them that the textbook could not be located, and since it could not be located they could not pay me for the book.  I had previously received confirmation emails that the book had been received.

After more emails, I was assured that the check would be issued and should be received by me within 10-15 business days.  This was on 1/13/16 (and all of this started back in Nov. 2015).  Today is 2/9/16 and I still have no check, and I have no book.  Yesterday I sent Chegg another email asking where my buyback check is. Today I received an email saying I should have received it, and asking for my current address.  I emailed them my current address, although I have not moved and they have mailed multiple textbooks to me over the past couple of years.

Please beware of this company.  I have spent a lot of money with them, and will not use them for any further textbook needs.