I ordered a trainer from Bicyclebuy in Huntington, NY. They shipped it via DHL ground. The tracking says DHL left it on the front door, in plain view of the street. It is not there when I got back. DHL says the shipper didn't specify a signature, so their policy is to leave it at the front door.

Either they left it at someone else's door, or someone else liked the idea of using my trainer at their homes without my permission.

What recourse do I have?