centOS can't use yum update

As mencioned in previus post, I can not updare my centOS operative system hosted here.

Yum doesn’t find his mirrors :(

[root@cityplanner ndrini]# yum check-update
Loaded plugins: fastestmirror
Determining fastest mirrors
YumRepo Error: All mirror URLs are not using ftp, http[s] or file.
 Eg. 6.4 is not a valid release or hasnt been released yet/
removing mirrorlist with no valid mirrors: /var/cache/yum/x86_64/$releasever/base/mirrorlist.txt
Error: Cannot find a valid baseurl for repo: base

My sistem version:

[root@cityplanner ndrini]# cat /etc/*release*
CentOS release 6.4 (Final)
CentOS release 6.4 (Final)
CentOS release 6.4 (Final)
cpe:/o:centos:linux:6:GA

I tried this:

[root@cityplanner ndrini]# wget "http://mirrorlist.centos.org/?release=6&arch=x86_64&repo=os"
--2014-12-12 11:05:07--  http://mirrorlist.centos.org/?release=6&arch=x86_64&repo=os
Resolving mirrorlist.centos.org... 72.232.223.58, 204.15.73.243, 64.235.47.134, ...
Connecting to mirrorlist.centos.org|72.232.223.58|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [text/plain]
Saving to: “index.html?release=6&arch=x86_64&repo=os.1”

    [ <=>                                   ] 527         --.-K/s   in 0s      

2014-12-12 11:05:08 (61.7 MB/s) - “index.html?release=6&arch=x86_64&repo=os.1” saved [527]

But I get the same initial error. Is there any special setting in digital ocean I have to set?

Andrea