They would leave a voicemail in Mandarin. But here's the deal-I set my Android to only calls from contact list and they get through long enough to leave a vm. So I set it to only vm from contacts-they get through and leave a vm. Then I missed a call from someone that was not in my contact list that a friend had passed away.....
When I was on call for my work, it was impossible to get some rest cuz of spam calls. And you could only miss 2 calls i(AWOL) in your entire career.
I googled these calls and they are nationwide. It's usually a scheme aimed at Chinese that they need to get with the Consulate or get deported, or they need to pickup a package as part of this BS. That's why my vm usually started with a DHL Delivery announcement.
Like I have heard, the next big war won't be so much fighters and ships, but technology. Power Grids, Banks, Communication. Not going to be safe anywhere.