There are a few ways you can look at this. Technically, your article was copyrighted as soon as you wrote it and published it - online, in print, wherever.

I guess you need to decide if having your article posted on that website will help your business. If you think there's some benefit there, then contact the owner and explain the situation. Tell them they have permission to use this one article so long as they credit you (at the beginning of the article if you want - and add the link!), but to ask for permission before using any of your other articles.

If you don't want them to use your article, then write to them and respectfully request they remove it immediately. They did not get your permission, so they do not have the right to use it.

Best of luck on this!
Kathy