Unattended upgrades doesn't upgrade (or does nothing at all)

I've been trying to make the package unattended-upgrades running under Debian GNU/Linux (7.0) with no success so far.

The steps I have followed:

• Install unattended-upgrades

• Enable it

  sudo dpkg-reconfigure -plow unattended-upgrades
  

• Uncomment the following lines in /etc/apt/apt.conf.d/50unattended-upgrades

  "o=Debian,n=wheezy";
  "o=Debian,n=wheezy-updates";
  "o=Debian,n=wheezy-proposed-updates";
  "o=Debian,n=wheezy,l=Debian-Security";
  

• Wait two days

It's supposed to run every day, but it did nothing by the time. I've checked its logs at /var/log/unattended-upgrades/ and apt history log at /var/log/apt/history.log but nothing happened there since the installation.

Is there any step I am missing to enable it? After reading the doc under /usr/share/doc/unattended-upgrades/README, I think that the above are the only ones you have to follow to get it running.

Try this:

Unattended-Upgrade::Origins-Pattern {
        "o=Debian,a=testing";
        "o=Debian,a=stable";
        "o=Debian,a=stable-updates";
        "o=Debian,a=proposed-updates";
        "origin=Debian,archive=stable,label=Debian-Security";
};

The file /etc/apt/apt.conf.d/20auto-upgrades must contain:

APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Unattended-Upgrade "1";