How would you go about revamping a navigation as long as this while keeping all the links visible
You should group links together that are related to each other. Usually you could find a hierarchy. Like the one in your second image where WiFi could be the top category and ChangiWiFi, SG WiFi Router and SG WiFi Plan could be sub catogeories of WiFi. Do that with all the links and group them dogehter in subcategories like the example of WiFi.