Try following the steps in this article for deleting decks.
In order for decks to be deletable on the web, they need to have been published with a version of Haiku Deck made in mid November (when we released syncing as a feature) or later.
If you still have the deck on your iPad, just make sure your version of Haiku Deck is up to date, then tap EDIT for that deck, then return to the Main Menu (make sure you're connected to the internet) for the app to re-save your deck to the web. That will make the deck deletable on either your iPad or the web.
If that doesn't work, check the UPDATES tab on your iPad in the App Store, and make sure you have the latest version of Haiku Deck installed.
If you don't have the deck on your iPad, or you've checked all of the above and your decks still won't delete online, then please click the "submit a request" tab at the top of this page or email us the deck URL at email@example.com so we can remove the deck from our servers manually.