It should be in your purchase history unless you bought it when you were not logged into your account and checked out as a guest.
If that is the case, then you will have to find the email you were sent confirming your purchase and payment.
This will be in your personal emails, not your Ebay messages/email for this account.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)