You would need to stop the automatic updater as follows:
Run the following command
sudo dpkg-reconfigure -plow unattended-upgrades
You'll see prompt for Configuring unattended-upgrades :
Select No to disable automatic download and install of updates and press Enter.
This updates the config file
$ sudo dpkg-reconfigure -plow unattended-upgrades
Replacing config file /etc/apt/apt.conf.d/20auto-upgrades with new version
$ cat /etc/apt/apt.conf.d/20auto-upgrades
For more information on configuring packages, see man dpkg-reconfigure
Configure a package which has been unpacked but not yet config‐
ured. If -a or --pending is given instead of package, all
unpacked but unconfigured packages are configured.
Configuring consists of the following steps:
1. Unpack the conffiles, and at the same time back up the old
conffiles, so that they can be restored if something goes wrong.
2. Run postinst script, if provided by the package
dpkg-reconfigure - reconfigure an already installed package
Specify the minimum priority of question that will be displayed.
dpkg-reconfigure normally shows low priority questions no matter
what your default priority is. See debconf(7) for a list.
Reconfigure all installed packages that use debconf. Warning: this
may take a long time.
Prevent dpkg-reconfigure from reloading templates. Use with caution; this will prevent
dpkg-reconfigure from repairing broken templates databases. However, it may be useful
in constrained environments where rewriting the templates database is expensive.