Contact your state or county agency that registers business names and entity types. If you registered only the business name and were operating as a sole proprietorship, that may have expired long ago. In some states a DBA is good for only 5 or 10 years. Generally, you are not notified when a DBA expires. You might do an internet search to find the web site of your state agency and see if the site contains a 'search' function. If so, you can plug in your business name and see the history associated with the name. It would show when you registered the name, when it expired (if it has) and when the other person registered the name. It will also show the other person's name and business address. In some states it is legal for more than one sole proprietorship to have the same name, but not for LLCs and corporations to have similar names. If you were a corporation or an LLC, you must file an annual report form to keep your business active. If you fail to file the form every year, the state can administratively dissolve your business and you have a limited time to in which to reinstate it. It sounds as if you are not using the business name and haven't for some time. If so, and you want to get back into business, you may find it easier to register a new name.