If the seller has not mailed the item within a few days of payment, you can open a Claim for Item Not Received.
If you can't, go to the credit card *you paid with and start a chargeback.
And in future read the entire listing including the Shipping Returns and Payments page which gives the window for delivery.
*The safest way to buy anything online is with a credit card backing a Paypal account. This gives an eBay purchase three levels of Buyer Protection.
Debit cards, bank accounts, etransfers, prepaid or gift cards are like sending cash in the mail. It is impossible to get your money back.