I added a robots against facebookexternalhit/1.1 and after a while the hits stopped. An interesting point is that my website had an error regarding the canonical url and the og:url meta, which basically created a link to a non-existent page. If the page /x was accessed, og:url would be /x/y and if /x/y was accessed then og:url would be: /x/y/y and so on, perhaps this was one of the causes. Although Facebook accesses were repeated on the same pages already accessed.