WALMART PLUMSTRUCK They refused to provide me with a refund of $335.00 on merchandise I returned unopened. Internet

I ordered a weight distributing hitch through Walmart for $ 335.00. I received the hitch and realized it was not sufficient for my application. i contacted Walmart and asked to return it. They informed me I would need to contact Plumstruck, which i did. they told me to UPS it to Curt MFG in Wisconsin. I sent it UPS to Curt and they received it on 10/19/2012. It was signed by MOHR. I had insured it and requested a signature upon arrival. It cost me in excess of $ 110.00 to return it.Now Walmart won't deal with me and keep referring me to Plumstruck. Plumstruck keeps saying they will refund  when they receive confirmation that it was returned

I have contacted Plumstruck with my UPS tracking number and who signed for it and still nothing.