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For the contacts to show properly, you need to have a menu item where your contacts would show. Create a menu item that will show the category (or all the categories if your contacts are from several categories). You probably don't want this menu item in your menu but it needs to exist in order for the contacts to load in a page fit for them. Add .item-xxx {display:none} to your template stylesheet. This way, the menu item won't show (xxx is the menu item ID for the menu item created).

Hello,
what is the menu item type of your 'contact us' link? Are your contacts in a same category or are they from different ones? It is difficult to diagnose your problem without knowing your configuration.
For your contact links to work properly from the Trombinoscope component, you need to have a menu item associated with each contact category, as the standard Joomla! framework requires an existing page to show the contacts into. The previous solution also suggests hiding these menu items from the menus in case they are not wanted.