calculated column – My Sharepoint formula not working

=IF((Sett. Start)<=Today,"Visit Due",IF(ISBLANK((Visit Notification No.)),"Visit Not Due","Visit Done"))

I am using above formula in SharePoint List but it is working partially. I am not getting result as “Visit Done” if (Visit Notification No.) is not blank and I am getting same “Visit Due” as result value.

Please suggest.