As advised, with Simple Delivery, Ebay refund the buyer if items don't arrive.
Check in 'payments' to see if the buyer's payment has been released to you.
If a few days have passed from receiving Ebay's message, contact Customer Services.
Tell them the item was sent using SD and never arrived, that Ebay refunded the buyer and you are still waiting for payment.
There are a lot of complaints about SD, but this is a huge benefit to sellers who no longer have to try and claim from reluctant carriers when things go missing.
"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)