I've gotten this many times.
If you pick up there's silence. If you don't pick up, they won't leave a message on your answering machine. If you call back immediately you get a recording that all representatives are busy and if you want to be placed on their DNC list state your name and number. Scammers can use and manipulate your recorded voice. I just started repeatedly calling them back and leaving a 1 word voicemail: "[***]."