How to deal with an uncooperative seller about a return and refund?

[vongy10]

So I bought a computer case called the Fractal Define R5 as it was advertised. Receieved an R3 which is an older model. Contacted the seller and told them the wrong case was sent. They told me I should just accept it and it's 'practically the same'. I refused and opened up a return case. After some arguing the seller agreed to a return but wouldn't pay for it. I agreed to pay for half of the postage but they refused to send me half so I sent it via COD and the seller has told me they will not accept the return and it will be sent back to me. I've told them that I will not accept it either.

Anyone know what will happen with this case? It's unfortunately not in the resolution center, just the return case. I'm afraid that I'm not going to get my money back and neither of us will have the computer case. I was being professional about this situation and they were just trying to weasle their way out of it. It wasn't a company or anything just a regular seller.