Victim of automated dialler?

[Osem]

Hi all - I keep getting calls from what appears to be the same number (although 1471 doesn't log it) every weekday at around the same time. I'm fairly certain it's the same number as nobody ever speaks but I can hear what appear to be the same or very similar office type sounds at the other end before the line goes dead.

I rang BT and after navigating a protracted series of automated menus wound up registering with the telephione preference service which, to be honest, I believe I registered that same line with some years ago.

The line in question is a home business line so I do like to answer incoming calls if at all possible so is there anything else I can do to stop this happening?

Cheers as always!