I put a large piece of furniture up for auction last week, listed as collection-only and cash payment on collection. The winning bidder didn't contact me, so I sent them a message asking to arrange collection and payment. No response to my message, or to a follow-up the next day, but the buyer has now paid by PayPal (despite me requesting cash payment). I've messaged them again, pointing out that the item is collection-only. Still no response. Any advice on what should I do next?