@mashatucke_0
< the seller won't respond to me and hasn't shipped the item >
It's difficult for me to comprehend how you know the seller hasn't shipped the item if the seller hasn't told you so. If you're relying on tracking updates – or lack of – tracking is unreliable. Oh, sure, it's comforting to watch tracking report your item from point to point as it makes its way to your home ... I like to do that myself. But it isn't a requirement, and when tracking isn't available I just do without. The fact is, tracking is actually for the seller's benefit, it's the seller's only protection against fraudulent "item not received" claims.
The buyer's protection regarding non-arrival of items is eBay's money back guarantee. Check the estimated delivery date, or range, in the order details on your Purchase History page. Don't click into the item link itself, make sure you're looking in the order details. If that date passes and you haven't received your item, then you can open an Item Not Received claim. That was explained very well to you in the Reply above.
There have been complaints lately about certain post offices taking a lot longer time than usual to deliver mail. There are reasons for this, but I won't go into that. If your delivery has been delayed beyond the ED date, and you file for and receive a refund, there's a chance that your item will eventually be delivered. Better late than never, eh. When that happens, it's your choice and on your honor to repay the seller, because eBay won't compel you to do so.
