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Depending on your carrier, some carriers have spam blocking apps as part of the service that allow you to block by category, and one of those may be private calls. You might check that, or also an app like Truecaller might help.
 
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Reactions: The Cockney Rebel
Y’all I use the scam blocking feature from my carrier.

For iMessages I use Textkiller to block iMessages and text messages from unsolicited numbers.
 
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