Today I noticed I had unintentionally scheduled the same item for sale twice. I had difficulty trying to delete the duplicate listing. Other buyers have had the same difficulty. The advice, from 3 years ago, to go to scheduled listings and delete the duplicate is no longer available.
Here was my fix. I opened the duplicate and--because I had another item I could list in the same category--deleted all the information from the duplicate listing and filled in information for the new item. I believe this worked because I utilized the item number eBay already assigned for the auction.
Or, and I didn't try this, enter "End a listing" in eBay's seller Help. I was presented with a list of all my scheduled items and it seemed I would be able to work through that.