Hi @Flagpole I had three calls like this today myself but I hardly ever use the landline so when it rings I'm almost certain it will be one of these types of calls, they're a nuisance all the same. BT offer a free service called Call Protect which may be useful for you check out this link for more info.
There are also call blocking phones on the market that screen the calls before they reach you which seem to be very effective in preventing these calls as most of the scammers hang up when they're asked to announce who they are.
I would recommend the call blocking phones wholeheartedly. After buying a set just over a year ago, not a SINGLE nuisance call has got through. Any genuine callers not in my contacts list have been prepared to announce themselves. For some reason, scammers choose not to! And pre-recorded massages are unable to, so they get stopped in their tracks at the first hurdle! Silence is golden... 😁