Illegal string offset in PHP function in via Theme Customizer

I have this setting in wp_customize:

        // Select share box options.
    $wp_customize->add_setting( 'single_share_box_options',
    array(
        'default' => $this->defaults['single_share_box_options'],
        'transport' => 'refresh',
        'sanitize_callback' => 'quanticthemes_text_sanitization',
        'active_callback' => 'quanticthemes_share_box_condition',
    )
    );
    $wp_customize->add_control( new Customizer_Simple_Checkbox_Control( $wp_customize, 'single_share_box_options',
    array(
        'label' => __( 'Share Box Options', 'custom' ),
        'description' => esc_html__( 'Select share box options.', 'custom' ),
        'section' => 'single_post_general_section',
        'active_callback' => 'quanticthemes_share_box_condition',
        'input_attrs' => array(
            'sortable' => false,
            'fullwidth' => true,
        ),
        'choices' => array(
            'facebook' => esc_html__('Facebook', 'custom'),
            'twitter' => esc_html__('Twitter', 'custom'),
            'linkedin' => esc_html__('Linkedin', 'custom'),
            'pinterest' => esc_html__('Pinterest', 'custom'),
            'telegram' => esc_html__('Telegram', 'custom'),
            'email' => esc_html__('Email', 'custom'),
            'whatsapp' => esc_html__('WhatsApp', 'custom'),
            'link' => esc_html__('Link Box', 'custom'),
        ),
    )
    ) );

Then I try to output like this:

        $social = CustomTheme::$options['single_share_box_options'];
        <?php if( $social['facebook'] ): ?>
        <div>My content</div>
        <?php endif; ?>
        <?php if( $social['twitter'] ): ?>
        <div>My content</div>
        <?php endif; ?>

But I get "Warning: Illegal string offset ‘facebook’ ….
Any help please?