Unable to use yum repos whether with baseurl or mirrorlist in CentOS 6.5

Since a couple of days, I'm unable to retrieve repositories data with Yum, in my CentOS 6.5 server.
I did yum clean all a dozen of times, it emptied all but didn't solved the problem.

I tried to retrieve things by restricting to the single base repo :

yum --verbose update results in :

And when I configure a baseurl instead of a mirrorlist, I get this :

The server pings mirror.centos.org and I can reach without any problem the mirrorlist and the repomd.xml in a web browser. Disabling the plugins changed nothing.
The mirrorlist gives a 403 error and a baseurl 404...

rpm -q --verify -f /etc/yum.repos.d/* results in :

« n'appartient à aucun paquetage » means « doesn't belong to any package », in french...

Those problems occur with whatever repo I enable/disable.