Lizzy..Change your ebay password NOW!, if you have not already! This did happen to my friend, someone put a motorcycle on her listings and she was selling polo shirts. Also contact Ebay and let them know, so you can get a credit, if you have been charged. This is serious. I would also change your paypal password there too. If you have one. Looks as if someone has your password. Also after changing your password on ebay you'll need to get a new token here on Auctiva. Becareful and change your password often, some say about every 3 months to be safe.
Ask ebay how to go about ending that item, will they do it? Or do you have to?
Good Luck..let us know what happens.