That sounds like a fault with Royal Mail's system.
When is the item supposed to be delivered to you?
If you check the email you got from Ebay when you paid, what is the latest estimated delivery date?
"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)