I'm sorry this happened to you.
I hope you get this worked out and aren't out the expense. Did you have someone else bidding too? You might be able to give another bidder a second-chance to buy without it costing you anything.
But expecting immediate payment doesn't always happen. While I realize this isn't your current situation. Most sellers state how soon they expect payment. I usually say within 5 days or within 7 days, as sometimes people are watching more than 1 item you might have listed. Also, sometimes people win and aren't near the computer - I know that has happened to me as a buyer. Matter of fact I won something yesterday and I haven't paid for it yer
If you list something, you need to include how soon you expect payment as one of your conditions.