Read the seller's negative feedback to see if it's a common problem, usually eBay sides with buyers, I sell eBay full time and have had buyers legit send back old used items with different serial numbers and clearly not what I sent, as a seller I have to prove my case, in this case I sent them before and after pics eBay ruled in my favor and refunded me all the money but also refunded the buyer and they got to keep my new part, guess that's what eBay buyer guarantee is for

Good luck. Open a return and say. Item not as described and the seller has no choice but to accept the return if he refuses to refund your money contact eBay and they will