How long since you paid? I'd give it a week or so then contact the seller to chase. One more week for a response then contact Ebay. If it's lost in the post, the seller can claim a refund via the Royal Mail, as I've done in the past, then refund you.
You don't live in the Highlands do you, by any chance? If it was you who bought a size 14 Cherokee t-shirt from me 2 weeks ago, then I'm really sorry but I only got it in the post this morning!!!