There are more than 3 files to the IS module. Maybe you should download again and try installing it again.
If you want to manually delete the database entries, they are in the "configuration" table. You can see what they are by looking in the "install" function at the end of the /includes/modules/payment/internetsecure.php file.
Perhaps you have a zone setting in one of your modules that prevents deliveries to certain areas.





