menu appears, but no menus in Appearance-menus

I am converting a html/css site into WP, so I am keeping code here and there. I use sass and singularity for css, and have splitted the html index.html into php files.

I have removed the 3 existing html menus, and registered 3 menu names in functions.php. In Dashboard/menus I created one menu and picked some available pages as items in that menu. At a certain point (after installing a search plugin, I think), I noticed the menu had an extra entry (named after the name of that plugin, precisely)

I decided to start the menus from scratch, and deleted the menu from Dashboard, but the menu keeps showing in the front page, intact, with all the options.

How can I proceed to effectively delete it?

thanks