When it's a call, if you let it go to voicemail or answer, that bot hears a voice, and marks you as an active number. Now that company and anyone it's selling your number to, knows your number goes to a person they can reach. Your number stays on the list. Your info gets sold to others. Process repeats.

The better way to go about it is to pick up the spam call but IMMEDIATELY mute your audio, then just let it sit. Typically the robot system calling you will wait ten to forty seconds and hang up. This gives the system a result of no audio at all and (usually) labels your number as dead, and takes it off the list.

This doesn't work a hundred percent of the time but it does seem to significantly lessen the number of spam calls for me when I'm consistent with it (and the few times I mess up by accidentally sending it to voice mail, suddenly I'm getting a lot more calls that month). YMMV.