Sending unknown callers to voice mail automatically?
You can use "Do not disturb" mode judiciously. You can set the DND period to be effectively 24 hours, and add a contact group to the list of people who you will accept calls from. That works well for me. If someone calls you a second time, they will be allowed through - which works because the spammers generally only try once.

I agree that spamming has become downright silly.

Check with your carrier...they may have the ability to auto-block known robo caller numbers.

The problem I've been experiencing is that they spoof the number they're calling from and it's always different.

Good luck!