In the past two days alone, I've gotten over 20 spam calls with none of them leaving a message. Just 3/4 seconds of silence on my voice mail. One call the other day left a 22 second blank message.
Hmm - I have a Pixel as well. I've been blocking / reporting but they seem to come from tons of different phone numbers. And for some reason the Pixel lets them leave a voice mail if they're blocked / known spam.