Pi-hole not working

Are you not curious?
If no RA's are advertised on your LAN (could be any device in theory), you should see something like below:

pi@ph5b:~ $ rdisc6 eth0
Soliciting ff02::2 (ff02::2) on eth0...
Timed out.
Timed out.
Timed out.
No response.

EDIT: But if there are:

$ rdisc6 eth0
[..]
 Prefix                   : fd00::/64
[..]
 Recursive DNS server     : fd00::3ea6:xxxx:xxxx:xxxx
[..]
Source link-layer address: 3C:A6:2F:XX:XX:XX