Hang up on them. Do not say anything to them, just hang up. It's a variation of the "Yes" scam. Do not utter a word!! Just hang up. It really doesn't seem worth it to add numbers to the blocked caller list. If we don't recognize the number, we simply connect and hang up on them.
I just got a call from 740-217-1481 indicating they were from the IRS and it was a final notice before I would be sued....I have been dealing with the IRS and their numbers are very different and they send letters with correct numbers if you do need to contact them....I hate Fraud.