Apache shows general root index rather than DocumentRoot index configured with Virtual Host in Debian

I have multiple websites supposed to run each with its own domain (e.g. site1.com, differentsite2.com, othersite3.com etc.). The operative directories of each website are dedicated subfolder in /var/www/html/

e.g.

/var/www/html/site1
/var/www/html/site2
/var/www/html/site3

The virtual host for each website is something like

<VirtualHost *:80>
    ServerName site1.com
    ServerAlias www.site1.com
    DocumentRoot /var/www/html/site1
    <Directory /var/www/html/site1>
            Options Indexes FollowSymLinks MultiViews
            AllowOverride None
            Order allow,deny
            allow from all
    </Directory>
</VirtualHost>

with a dedicated config file in /etc/apache2/sites-available/ enabled with a2ensite command and the default config disabled with a2dissite 000-default.conf

others website are configured in a similar way with

<VirtualHost *:80>
    ServerName site2.com
    ServerAlias www.site2.com
    DocumentRoot /var/www/html/site2
</VirtualHost>

etc.

Problem:

When I open www.site1.com rather than showing index in its DocumentRoot at /var/www/html/site1/index as supposed, It shows the index in main root at /var/www/html/index

Could someone help he to understand the issue?

The issue was caused by the fact Apache server was configured on port 8080 and Nginx on port 80 so when I invoked the site on port 80 the invocation was processed by Nginx.