Those seem to be Charter/Spectrum DNS servers.
With IPv6, your router may well be advertising its own DNS server(s), often its own IPv6 address, and thus any device may by-pass Pi-hole via IPv6.
You'd have to find a way to configure your router to advertise your Pi-hole host machine's IPv6 as DNS server instead.
You'd have to consult your router's documentation sources on further details for its IPv6 configuration options.
If your router doesn't support configuring IPv6 DNS, you could consider disabling IPv6 altogether.
If your router doesn't support that either, your IPv6 capable clients will bypass Pi-hole via IPv6.