Setup a whitelist, I think it's native on iPhone and there are multiple Android apps. Only calls from your contact list will ring through. My voicemail is, "You're getting this because you're not on my contact list, send a text and I'll get back to you."

I just block and report as spam any spam text messages I get and any calls that get marked as scam likely. It was terrible before the election because I live in a swing county in a swing state and I think everyone was just mass spamming every number in the area code, but since then I haven’t really gotten much, maybe one errant text every 2 or 3 weeks. Which is much better than it was last spring and summer when the amount started picking up for me.