Both really. Some display as “spam risk”.
From what people are saying I guess there’s no way to completely stop it.
If the call displays a number then its hard to block it on a stock android without a lot of work to construct white lists.
I have never done it.
Yeah I feel your agony.
What I’ve done is put the phone on silent notifications and then check list of calls and Voice mail every so often. If they aren’t in my contacts and didn’t leave a VM then tough luck to them. ha ha