For landlines, we've recently changed to BT phones with Call Blocker. It does mean you have to identify all the callers you want to hear from e.g. surgeries as well as trusted people. All non-listed callers go to voicemail (so far we've received no voicemail messages - surprise, surprise) and, for those you've mark as blocked, you hear nothing. It's been a godsend.
apg - I have looked at sister's mobile 02 phone and we decided to just sort of try to delete like a chippie number, we selected but no "block this caller" comes up.
just
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Delete
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1. Click on the 'contacts' number.
2. Click on the person making the nuisance call.
3. Click on the 3 dots next to the pencil icon.
4. Click 'Block Number'.
That should do it.
If the caller is not in the contact list:
1. Click on the phone icon as if you are going to make a call
2. Click on 'call history'.
3. Scroll down to find the number of the nuisance caller.
4. Click on the three dots next to the number.
5. Click 'block number'