Why user is added back in database after deletion?

I solved this by doing something link

$hook = add_menu_page('My Plugin Settings','My Plugin Settings','manage_options','my_plugin_settings','display_plugin_options');
add_action('load-'.$hook,'do_on_my_plugin_settings_save');

function do_on_my_plugin_settings_save()
{
  if(isset($_GET['settings-updated']) && $_GET['settings-updated'])
   {
      //plugin settings have been saved. Here goes your code
   }
}