You made a mistake (two actually) and the seller is not required to refund the shipping you paid.
As you now know, when the Claim is Not As Described, that is the seller's problem and they pay the shipping.
When the Claim is Buyer Remorse, which you chose, that is the buyer's problem and they pay the shipping.
You can try opening a Facebook account for the one day or so then closing it when you no longer want it.
The clerks assigned to Facebook do seem to be the most responsive but there is also an eBay Chat.
https://community.ebay.com/t5/Selling/How-do-I-contact-Customer-Support/m-p/32016431#M1783851 -> Automated Assistant, type AGENT -> enter. You will then get more options.
The social media Chat accounts are covered by trained eBay employees with some authority.
And you get a transcript so you can compare what you heard with what you were told.
https://www.facebook.com/eBayForBusiness/ — Message button in upper right on landing page.
https://twitter.com/askebay?lang=en