You do not contact eby, after 4 days, on day 5 you cancel the sale using reason BUYER DID NOT PAY, they get a strike, you do not pay a selling fee and no feedback can be left.
I SUGGEST you use HELP AND CONTACT top of pages and enter UNPAID items, and read. The need to contact ebay is rare, as all these situations happen every day and sellers deal with them, without bothering ebay.