Example: this post has 27 likes on Facebook right now:
https://www.facebook.com/160210837333829/posts/712679778753596
but if I check the link with the Facebook's Like Button Plugin it says 0 likes. Why? Should I insert another link?
I hope I understood your question right.
The like button plugin takes the url, which you gave to it and counts how many times it appeared in a post and was liked, how many times it was shared, commented and so on at the facebook page. That means, if you give the url http://www.example.com/, it will count all the likes, comments and shares that were given/made to a post which include this certain url.
So, probably your post has 27 likes, but the page you checked with the plugin (the facebook-url, it's not the same as the post!) does not have been shared, liked or whatever on facebook itself (I know, it's a bit complicated).
I think the better alternative for you would be embedding the post. Here is a nice tutorial for this.
Hope this helps!