You should contact the editor of your category. They probably thought that your site doesn't fit there anymore.
The editor contact details are not publicly displayed. To contact your category editor simply browse to the category and scroll to the bottom of the page where it will state the editors username. Click this to view thier profile and on that page you will find a link to send an email message to them. If your category doesnt have an editor listed then you will need to drill backwards through the structure until you find an editor in a category at a higher level. In future please post your DMOZ related questions in the correct sub forum.
Did you change anything in the site ? Did it change subject/theme ? Does the category you belong in seem to be overcrowded ? Don't bother contacting particular person just resubmit to the correct category but if the category seems to be overcrowded then you don't have much hope ...