I uninstalled all libreoffice but the update manager still shows libreoffice updates, (I uninstall it from software center).
How do I remove this updates or remove libreoffice completely?
As this Ubuntu wiki page says:
Starting with Ubuntu 11.04, LibreOffice is part of Ubuntu. Since LibreOffice is already part of the standard packages..... if you're using Ubuntu 12.04 LTS, your LibreOffice version is 3.5.2. Only security updates will be applied to it, while feature updates for greater versions will be available by using the PPA.
Since it is part of the standard packages and PPA you cannot disable security updates.
Go to Ubuntu Software Center > Edit > Software Sources > Other Software and delete any ppa of libreoffice.
You can also try:
sudo apt-get remove --purge libreoffice*