Seller did not refund Return Postage

[spider_xo]

Hi

Just a few questions please.

I bought an item listed as New/Demo from the States for US$335 (including postage cost of US$35) but actually the seller was from the UK and when he sent the item to me it was not as New/Demo condition but a second-hand one. I have talked to the seller and returned the item to the UK whick cost me AU$47. Ebay advised me that the seller was responsible for the return postage as the item didn't match the listing description and the seller also agreed to pay for the return postage at first but after he got the item back he only refunded me US$335 and not the AU$47 return postage. I have sent him a message about this but he did not respond. My questions are: Should I open a case and if I so, will I get my AU$47 back? 

Thanks.