Who is responsible to returning an item that was not ordered?

I recently ordered an exercise pen from a Pet Supply Company through E-Bay. The company totally messed up. I had gotten an e-mail from them that the order had been shipped the next day. Three weeks later, it still had not arrived, so I attempted to contact the company. After several e-mail and a couple of phone calls I finally got to talk to someone. She checked on the status of the order and discovered that there was a mistake and the order had not been "keyed in" to their supplier. I asked for a tracking number and FINALLY received two, along with another e-mail saying that 2 pens had been shipped, and directing me to refuse the 2nd one. I was not home when the order arrived and the UPS guy left both on my porch. Wanting to do the right thing, I contacted the company again and explained the situation, they said they would contact their supplier and have a shipping tag sent to me so the extra kennel could be returned. Weeks went by again with no tag...called again. I was told to contact UPS and arrange to have it picked up ( I cannot lift it to take it to a UPS store since it is very heavy and I have had surgery.) I was told that if there was a fee they would reimburse me. I called and there is indeed a fee totaling almost $12. I have spent several hours on the phone with the Pet Supply company, their supplier, and UPS. I feel that I am being given the full responsibilty to arrange for the return and considering the track record of this company for getting back with me, I don't trust them with reimbursement. An operator with the supplier said if it was his company, he would just tell me to keep it-but can't do that since the Pet Supply Co. I ordered from is the one who must make that call. What are my rights? If I refuse to arrange for the pick up of the item I did NOT order and pay the pick up fee, can they come back at me? I feel it was not my mistake and therefore not my responsibility and I have made a good faith effort to return item. Any web sites offering free legal advice about this sort of thing?

Ariel, thanks! I have received a shipment tag, but I have had such a bad track record with getting responses from this company. (They have dropped the ball at every single step of the way.) I've had to constantly contact them to let them know about the issues with the return. I simply do NOT trust them for the $12 reimbursement. I'm fed up with the whole thing and am ready to just say "if you want it, come and get it". I'm wondering if I am responsible for paying the pick up fee for the unordered item. It doesn't seem fair since they've totally goofed this whole process.
Anyway, thanks for info.

Call them again, get a manager, and explain the situation. THEY made the mistake, if they want it back, they do the leg work.....shipping label, arrange for pickup, contact ups. Can they come back at you? Hmmmm..........they do have your paypal account # or something. Contact your financial institution or paypal....ask them. Sounds like your ok to me. Good luck with it and don't take any gruff off those bastards!

I am not sure about any websites with advice, but since they messed up and ordered the item twice, then it is their responsibility to pay for the costs associated with bringing the extra one back. That is how my company does it if an order goes out and is wrong; the item(s) that were received in error are picked up at our cost.