Why don’t we use CAPTCHA for robo spam calls?

So when a new number calls you: your service provider instantly prompts the caller via automated message asking them to input a random 0-9 random digit code to give access for the call to go through. Robo callers can’t think so the call won’t go through.

This doesn’t effect anybody because pressing a random digit takes zero effort and if it’s a saved contacts then they don’t need to be promoted.

This should be an optional service since not everyone is bothered by robo calls.

This would typically be used for landlines. But cellphones can benefit too.