Hello J.Wall,
I apologize for the inconvenience but here is the state. Avast for Mac has been historically existing in following versions: 5,7,8,9, and 2015 (internally 10). Versions 5 and 7 have been asking users to allow an update. Since we couldn't maintain the virus database in an old format any more, the last update of Avast version 7 started automatic updates. The option to opt-out automatic updates through the checkbox has been added to version 2015, if I recall well, and it should be respected. If not, please let us know, it would be an important bug.
If your aim is to silence a Cisco VPN only, you can block a connection to an update repository download.ff.avast.com (i.e. by redirection to 127.0.0.1 in /etc/hosts) and install the old program version.
However, if you would like to use Avast as a computer protection, there is no other option than to contact your system administrator to reconfigure the Cisco VPN.
Best Regards,
Martin