not getting API setting saved confirmation message after update on option page

You need the settings_errors(); function somewhere on your settings page:

function display_acme_options_page() {
    settings_errors();

    echo '<h2>Acme Options</h2>';      

    echo '<form method="post" action="options.php">';

    do_settings_sections( 'acme-options-page' );
    settings_fields( 'acme-settings' );

    submit_button();

    echo '</form>';

}