Hopefully you're still in time to open a case for item not received so proceed this way.
Go right of the item purchased, and from More Actions select.... I Have Not Received My Item.
If you are not fully refunded within 3 days, you must escalate the case on day 4 or within 30 days from opening the case, and eBay will step in and force the refund.
Do not close the case early for any excuse or promise the seller may give, and do not forget to escalate.
If the time has passed to claim with eBay, turn to your payment provider for help with your refund.
@noumou_0