Where did my voicemail go (VZW)?

There were two new ones from that night that I hadnt listened to yet (VM icon was on when I went to bed), and a few random saved ones. Nothing important, private, or remotely interesting.

The phone lit up 1 min after the ignored Restricted call with the VM icon going away, as if they had just been checked. I immediately called VM and all new and saved messages had been cleared.

I called customer service today and whoever was on the other end was about as useful as a clogged toilet.

How would I pursue a court subpoena to obtain the number that called? This in itself isn’t that big of a deal if it is isolated, but I’d obviously like to know whats going on.