Barnstormers (Equestrian Products)
Company will not respond to request for action

I made a purchase through this company's online store. (I live in the USA). The item I purchased was important enough to me that I was willing to pay shipping to the US. The company sent me the wrong size of an item for my horse. When I contacted them, they instructed me to return the item to them for an exchange. I emailed them asking how to proceed, because I did not think I should be responsible for paying the shipping charges since it had been their mistake. I have emailed them since then, and they refuse to respond.