Update/Upgrade from NC12 (12.0.0.49) to NC13 - updater did not run through - problems

Hi guys n galls,
I used the updater app from the Web to upgrade from NC12 (12.0.0.49) to NC13 (13.0) on March 14th.
Sadly, it didn’t ran through, in the sense, that there is no NC13 on the server now. The updater told my it was. The web interface was not reachable and config.php told 12.0.0.49 still.
There is a updater.log available in a folder, but I could not make out any errors thereof. The updater has also created a backup automatically.
I made another backup of the nextcloud folder structure and used the backup from the updater to copy that back to /var/www/nextcloud.
Now I could login on the web interface and I was able to click on update to 13.0.0.1, bringing my to the updater page, which stated, that the 13.0.0.1 archive was downloaded and all checks were checked green already an the page - no update was possible.
I tried the same with the php app “occ” leading to this output:
root@odroid64:/var/www/nextcloud/updater# sudo -u www-data php updater.phar
Nextcloud Updater - version: v12.0.0

Current version is 12.0.0.

Update to Nextcloud 13.0.1 available. (channel: "stable")
Following file will be downloaded automatically: https://download.nextcloud.com/server/releases/nextcloud-13.0.1.zip

Steps that will be executed:
[✔] Check for expected files
[✔] Check for write permissions
[✔] Enable maintenance mode
[✔] Create backup
[✔] Downloading
[✔] Verify integrity
[✔] Extracting
[✔] Replace entry points
[✔] Delete old files
[✔] Move new files in place
[✔] Done

Continue update? [y/N] y

Info: Pressing Ctrl-C will finish the currently running step and then stops the updater.

[✔] Check for expected files
[✔] Check for write permissions
[✔] Enable maintenance mode
[✔] Create backup
[✔] Downloading
[✔] Verify integrity
[✔] Extracting
[✔] Replace entry points
[✔] Delete old files
[✔] Move new files in place
[✔] Done

Update of code successful.

Should the "occ upgrade" command be executed? [Y/n] Y
Nextcloud is already latest version

Keep maintenance mode active? [y/N] N

Maintenance mode is disabled

So, the version is still NC12 (12.0.0.49).

How can I upgrade?
Do I need to erase a cache from the updater app or something?
Or a cache or thelike in the database?

Thanks.