It’s possibly a RJ11 socket not a RJ45, they do look similar. If it’s a RJ11 then perhaps the property had the old ADSL service many years ago, before VM rid of that service, I think to Talk Talk. This could explain why the location had broadband and is still perhaps wrongly identified in the VM database.
Tudor
There are 10 types of people: those who understand binary and those who don't and F people out of 10 who do not understand hexadecimal c1a2a285948293859940d9a49385a2