If the parcels never reached the buyer and the tracking confirms they have been damaged and destroyed while in the 'care' of Evri, I think that with Simple Delivery, Ebay would have taken responsibility for refunding your buyer.
Contact Ebay Customer Services and explain what has happened.
Make sure they are aware that you have refunded the buyer. Get them to look at the evidence from Evri regarding the fate of the parcels.
Use the link to get a callback.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
"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)