If it's not showing in your eBay purchase,  then you may not have used it,  and bought as a Guest Purchase.

The best option is to get a new confirmation email using this link - https://www.ebay.co.uk/help/guest-order?topicId=4065&af=2.

From there you will be able to select the view order details,  and use this  to open a case if you need to later.

@gabriell4465