Hi Jiri,
I recommend you first check the effective security rules on the interface:
After that if you are completly sure that there no block trafic , execute a curl or wget to any file on that repository to verify if it's workin.
wget http://azure.archive.ubuntu.com/ubuntu/pool/main/p/pacemaker/libcib-dev_1.1.14-2ubuntu1.9_amd64.deb
curl http://azure.archive.ubuntu.com/ubuntu/pool/main/p/pacemaker/libcib-dev_1.1.14-2ubuntu1.9_amd64.deb --output package.deb
Let me know if there is an error message.
Cheers,
Luis Arias