Subdomain doesnt work on Apache 2.2 and Debian 7

Hello,

I want to setup a subdomain in my droplet, I read and follow this tutorial: https://www.digitalocean.com/community/tutorials/how-to-set-up-apache-virtual-hosts-on-debian-7

Yep, all right. But, not work for me.

First, I point the dns of my domain in godaddy to: NS1.DIGITALOCEAN.COM. NS2.DIGITALOCEAN.COM. NS3.DIGITALOCEAN.COM.

Then, I installed apache2:

#apt-get install apache2

I created the directory for my domain in /var/www/mydomain.com And for my subdomain: /var/www/mydomain.com/subdomain

I copied the file /etc/apache2/sites-available/default and name mydomain.com and other with name subdomain.mydomain.com (all in this same directory).

I opened the file mydomian.com and add this line: ServerName mydomain.com

And change this: DocumentRoot /var/www/mydomian.com

Then, the same for the file subdomain.mydomain.com

Add the line: ServerName subdomain.mydomain.com

And change this: DocumentRoot /var/www/mydomian.com/subdomain

FInally:

#a2ensite mydomain.com and #a2ensite subdomain.com

Then:

#service apache2 reload

But not work!

The domain : mydomain.com works great, very great, but the subdomain doesnt.

In my browser I see this error code: Código de error: ERR_NAME_NOT_RESOLVED

Well, I tried to set the subdomain in my droplet cpanel add this A record: A mydomain.com ip.ip.ip.ip

But nothing. :(

Why? ?

Ps. Sorry for my bad english.