DNS: there’s an A record for uk.billion.com which is 223.27.48.97.
Ping to it fails, but that doesn’t mean too much. Trying to connect to port 80, there is an http server there. But trying to talk to port 443 for TLS / https, that just times out. So it seems that there is a misconfigured web server there, or else the A record is wrong.
However, trying to resolve billion.uk.com just gives me nothing in the DNS. There is a record for www.billion.uk.com which is just a CNAME to billion.uk.com which seems to not exist. That was using my own usual DNS servers. So I got the same as you, I suspect.
Now it gets weirder. Using the DNS server 1.1.1.1, resolving billion.uk.com does give an answer: an A record pointing to 217.194.215.4
So it seems the DNS is inconsistent. Someone has changed something and the results haven’t propagate through, or who knows what?