Is this a Royal Mail posted item? Use that tracking to go on their website ,or the courier's website, to see the status of your item.
If it states tracking not recognised, then one day after your item's last estimated date for delivery open a case for item not received.
An un recognised tracking should not show delivery , after 3 days if not refunded escalate the case and eBay step in and force the refund.
@princeislam