How do I return an item if the seller has declined my return request

[h629267]

I ordered a computer and requested a return but the seller declined and case is closed. The seller said that it's unfair because they already paid for shipping and I want to return it AFTER I got it. I want to escalate this with an agent from eBay to see if they can help me file a dispute but I haven't been able to get a hold of anyone. How can I take further action? I paid with debit card if that makes a difference. I haven't opened the box.