Virgin Media. At the time I switched I needed more bandwidth for work - dealing with multi-gigabyte blobs all day; I was with BT, but BT wouldn't let me upgrade to a gigabit fibre connection, and the City Fibre network which is now everywhere wasn't yet in my street.

You can go to VM dashboard to disable the adult content filtering. It will then not block DoT and DoH.

Many ISP will also auto-redirect un-allocated domain names to their own websites. Others will ban most inbound connections with a port under 1000 to prevent self-hosting/video-surveillance users.

Annoying if you are trying to bring up a remote domain server, and thinking WTF while checking things out in dig. lol =)