You can send a revision feedback request. But many buyers ignore it.

After two weeks? you will need to contact eBay to remove unreasonable negative feedback. If you are an effective, honest seller then eBay will happy to assist you. 

P.S

I also replied to the buyer under the buyer's negative feedback. I described honestly what I efforted and did for the item to send to the buyer that eBay could see it.  It could help you to remove your unreasonable feedback.  Cheers!