If you have a Page for your business on Facebook, It’s always good to check for duplicate or unofficial pages. Sometimes they are set up by an enthusiastic fan or community member, and sometimes…Facebook just sets them up.
If the site has an administrator, a diplomatic approach would be to contact him or her and have a dialogue about the page. If it is a positive Page, thank them for their cheerleading of your business, and request to become the administrator. Perhaps the old administrator can have a role on the official page, or be recognized in some way. Then, per the business Page Facebook settings, “…you can merge Pages you manage if they have similar names and represent the same thing. The likes and check-ins from these Pages will be combined.” Learn more. If the administrator of the page will not join forces with you, you can reqest that the page be deleted, though be aware that this can lead to some bad blood.
If the Page is unmanaged, you can claim it and merge it with your official page. You will have to answer questions proving you are the owner of the business.
If you have had experience with an unofficial Facebook page, please tell me about it in the comments. How did you handle it?