We used to get this problem so frequently that we decided to take action. We bought a trueCall telephone screening device which lets through without interruption all our approved callers, but forces all unknown callers, with either an unrecognised number or a withheld number, to record a name before allowing the telephone to ring, when we have the option of rejecting the call, flagging the caller as blocked permanently, flagging the caller as permanently accepted, or accepting just the current call.
We have found that scammers are very reluctant to record anything, probably fearing that modern voice analysis could identify the individual. Since installing the device several years ago we have been interrupted by only a handful of nuisance calls. The online call log shows that more than a third of callers hang up without us being disturbed in any way. The majority connect without interception, having been added to the approved list.
The device also records calls, which can be picked up remotely, making a separate device redundant. The level of screening can be tuned according to personal circumstances. I have no connection with the manufacturer or any vendor, except as a very satisfied customer, enjoying freedom from unwanted interruptions.
