Has a reasonable time passed your item's last estimated date for delivery, and you have not received the item?
Then, if the seller is not being helpful, go right of the item purchased, and from More Actions select.... I Have Not Received My Item.
If you are not fully refunded within 3 days, you must escalate the case on day 4 or within 30 days from opening the case, and eBay will step in and force the refund.
Do not close the case early for any excuse or promise the seller may give, and do not forget to escalate.
Be aware if the seller has a valid tracking number to show delivery, the case will close in their favour. Here, your first steps would be to ask household members/ neighbours if perhaps they took in the item. Was it Royal Mail delivery? Ask your postie where they left the item.
@yekinfagbem-0