You don't understand that law. Getting something that is different from what you ordered does not make the merchandise "unordered".
eBay's policy is what eBay's policy is. They will help you recover your original payment and shipping costs. If you want to bang your head against the wall until you violate the terms of their buyer protection policy, you have every right to do that, end up with no refund, and handle things yourself by, let's say, suing the seller in small claims court and traveling to the seller's state for court proceedings. Or you can accept the refund you are being offered through eBay's policies and, whoah, the seller may even pay you the return shipping costs. Worst case, you're out a few bucks for return shipping rather than having a small claims case that may cost you a ridiculous amount of money and time to obtain and may never be paid. Tough choice there.

