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OK, first things first: fix networking.
The ssh you are doing is most likely to your VM's console from the underlying host; that's why it isn't broken. You can use that to get in and fix the networking.
Edit the /etc/network/interfaces file as shown here:
https://docs.hetzner.com/robot/dedicated-server/network/net-config-debian-ubuntu/
Configure eth0. Give it the IP address, subnet mask and gateway address that Hetzner assigned you. Then, run "sudo service networking restart". You should now be able to ping your machine from the outside, and your other services may start working.
When upgrading Debian, it is only safe to upgrade from one stable release to the next major stable release (and then, reboot, and you can do the next upgrade to the next stable, and so on).