my return declined and eBay fails to do something

[bamidelowuy_9]

 I purchased 2014-2018 Toyota Corolla Stock Muffler 6000 Miles  from   jacobsilbert in Tampa Florida, on saturday night and I contacted him early on monday to canceled the order but he refused and send the item, I recievd the item and open request for return which he declined and he closed the request but ebay refused to offer any solution to this, I offer to pay back the shipping cost for the return but he refused, this is against the ebay return policy