It sounds like that may be due to either having a NameVirtualHost line in /etc/apache2/apache2.conf which looks like “NameVirtualHost *:80”, or that there’s another VirtualHost in /etc/apache2/sites-enabled/ using “VirtualHost *:80”, quite possible a default file names 000-default.
If you see a 000-default file, you can just remove it. If you see a “NameVirtualHost *:80” , you can comment that out.