Spam intruding on personal calls

Lately on my iphone 8S, Siri interrupts my conversations to announce an incoming SPAM call. It always happens when I am talking to one particular person. I have to click "Send Call To Voicemail" to get rid of the **** thing. All of my phone settings that supposedly govern this feature are set in the off position. The same spammer uses multiple phone numbers, usually 4 in a row. What can I do to stop it from overriding my settings?

Here's text from one of the voicemails left by the scammer: