Total rip-offs

I bought a dress from yellow sub, paid for it as well as shipping fee however the wrong dress was delivered. I advised them of this via their whatsapp number and they told me to send the dress back but at who's expense? I am now expected to pa for courier again whereas its their mistake and not mine. This is so frustrating as they have been ignoring my calls,messages,emails and delete my comments when I write on their facebook page. I need to have this resolved or atleast my money back please.