How long ago did you purchase the item? There are a number of reasons that could explain the seller's lack of a response - for example, if you only purchased the item a few days ago and completed the purchase late at night, then the seller may not even be aware that the item has sold, especially if he or she has been very busy at work since then and hasn't logged on to eBay since you purchased the item.
In the event that quite a bit of time has passed since you bought the item - for example, a whole week - then if the seller still hasn't replied to you by the time you read this response I would be inclined to suggest that you open an Item Not Received case. The seller will then have three working days during which he or she ought to resolve the matter with you from the date that the case was opened.
If the seller subsequently contacts you to make arrangements as to the date and time to collect the item, and gives you clear details as to where to collect the item from, then if the goods are exactly as described in the listing when you arrive to collect the item you can then just close the case. If, on the other hand, the goods are not as described when you arrive to collect them, or if the seller either fails to respond or replies but behaves in an uncooperative manner, then the best option would be to escalate the case to eBay four working days from the date that you opened the case in order to get eBay to step in and force a total refund of the money that you paid to the seller.
