Cases are not normally closed within minutes.

How did you respond when the case was opened?

The best option is always to accept the return and provide a label, then at least you would have the item back to sell again.  From looking at the buyer's feedback, it seems they believe you refused to deal with the return and they asked Ebay to step in.  If that happens, then almost inevitably, the buyer is refunded and told to keep the item.

I can see two possible avenues here.  

Speak to Customer Services again.  If you did not have any opportunity to deal with the case, then you could argue that they broke their own rules by refunding the buyer instantly.  Make sure you have to hand the email from Ebay stating a return had been requested, with date and time received, and then the date and time the case was closed.  If the case was closed within minutes, Ebay may possibly offer you some recompense.

Contact the buyer.  Be professional and polite.  Say you see they have been refunded and stress that the refund was paid by you and not by Ebay and ask them to return the items they bought from you.  You should offer to provide a label or funds for postage,