Received wrong item, issues with refund

[cinderpaw14]

I bought an item from a seller located in the USA, where the postage was paid for by eBay's international shipping programme. A package from the seller arrived yesterday and they have sent me a completely different item from what I bought (it's not even remotely similar). Opened a "wrong item received request with eBay and I've to send the wrong item back to the seller.

Ebay says the seller should pay for postage but I'm having trouble getting them to do that. I suggested they pay for the postage on Royal Mail's website and they can email me the label. Imo that seems the better option? Then I just need to obtain a proof of postage from the post office. But they're not responding to my suggestion of this. They kept telling me they will send me they money for the return postage, but I don't want to go pay for it until they give it to me first. Because it's going back to the USA, postage is around £18.00.

Then tonight, they said they would refund me so I can use that towards the postage. But uhhhh no. Yes I want refunded but I also want money for the return postage on top of that! So, I got my refund through there and it's only part of what I actually paid because they only refunded the item cost + postage cost to the ebay shipping centre (which is what the seller would have received when I paid) - I didn't get refunded for the eBay international shipping programme cost - which is about £18.00, since that went to eBay I guess.

This whole thing is a mess and to top it, eBay say the item needs to be returned by the 10th December. Which is making this return process more difficult because it's being returned to the USA, so it will take longer to arrive.

Why do I have to go through this whole mess when the seller made a mistake? Is there ever any chance I'm going to get the rest of my money refunded?