The Marketing tab is added by the woocommerce-admin package that is shipped with WooCommerce and can only be disabled by using filters as far as I know.
If you wish I can take a look, I need ssh and wp-admin access to the site, you can send details to admin at soft79.nl. Otherwise I recommend you to contact WooCommerce support as this is not related to our plugin.
The ‘Disable WooCommerce Bloat’ is hiding it, but disabling the plugin doesn’t show the Marketing tab, so there’s probably something else hiding it. Please contact WooCommerce support.