If you have already used our service:

This problem will never arise as our system automatically avoids duplicate submissions by keeping a permanent track of all previous submissions made.

If you've submitted on your own or using another service:

If you have the list of directories you've submitted to, you can upload the same by logging in and clicking on the 'Upload Submissions' link under the 'My Account' page. We will then avoid submissions to these directories.

If you don't have a list of the directories previously submitted to, you could still proceed with the submissions. Most directories don't accept duplicate submissions and would return error messages indicating that a link already exists; however, you would still be charged for these submissions.