Is my marriage to my former fiancée, after my parents rejected it, considered disobedience to them?

If the woman is religious and of good character, then strive to convince your parents to marry you to her, by interceding through relatives or others. If they refuse merely because she had previously broken off an engagement, then you are not obligated to obey them in abandoning her, and you will not be undutiful by disobeying them. However, if there is no harm to you in abandoning marriage to her, then it is preferable to obey your parents.