Hello,
If I think well, the 1st thing I should do is to prevent OpenVPN from starting at boot time and go back to SSH standard port 22.
Alas, I didn't manage to do that...
root@debian-live:~# fdisk -l
Disk /dev/sda: 300 GiB, 322122547200 bytes, 629145600 sectors
Disk model: QEMU HARDDISK...