I have received dozens of phone calls a day that almost-but-not-quite match the 'One Ring' scam. I get calls from international numbers, 'private numbers' and

I have received dozens of phone calls a day that almost-but-not-quite match the 'One Ring' scam. I get calls from international numbers, 'private numbers' and 'unknown numbers', (I'm not sure the difference between private and unkown, it's what android displays in caller id). The calls ring once and hang up. I've managed to answer it a few times but they usually disconnect before I can. When I answer I hear a few sentences in a language I don't recognize then they hang up. The unknown and private numbers don't match the 'One Ring' scam because you cannot call back a private or unknown number.