You can't delete it on your end... you'd have to contact whoever runs the website it's posted on. But if you sent something via email, did they say anywhere that they might publish it? If there was no indication, I don't think they can just put that on their website... I'd have to know more about it. If you do not wish to discuss this on the forum that's OK, you could email me or simply try your best in contacting the magazine through their website.
Some time ago I sent an email to an online magazine. My message was not something that I would have wanted others to see. To my surprise, when my name is searched on the web, this message is among the top 10 search responses. Is it possible to delete it from my end?