eBay has a specific process for unpaid items:
https://www.ebay.com/help/selling/getting-paid/resolving-unpaid-items-buyers?id=4137&st=3&pos=1&quer...
You need to read up on that process and follow it - if you do not it can affect your feedback, your fees, your sellers status, and even your ability to sell here.
Generally speaking, you can file an "Unpaid Item Dispute" after two days, and then close it after 4 more days. Once you do that, your fees will be refunded and you are free to relist the item.
