In Admin / Logs / Screened IPs you can make a Block rule for 2001:67c:198c:906::/64 - that’ll block anything on the local network he’s using.
If you want to block HERN Labs entirely, you could instead block 2001:67c:198c::/48, but the wider you get the more chance you have of hitting a legitimate user.
○ → whois 2001:67c:198c:906:2::256
% This is the RIPE Database query service.
% The objects are in RPSL format.
…
inet6num: 2001:67c:198c::/48
netname: HERNLABS
…