The buyer claims the envelope was poorly sealed, so it's unlikely that eBay will treat this feedback as unfair.
The reference to a refund doesn't mention eBay or PayPal, so it won't qualify for removal on this basis either.
I'm sorry, but unless you can resolve the problem with the buyer, and then send them a feedback revision request, you won't be able to get it changed. At least it's only neutral, not negative.
You might possibly be able to get the other feedback removed, where the buyer appears to be trying to complain that you don't offer combined postage. Buyers are not allowed to leave bad feedback because a seller refuses to offer something that eBay doesn't require them to offer, and eBay doesn't require sellers to offer combined postage.
