I had a missed call from this number. I called them back and they are a company that works for non-profits (I am also on the do not call list, so for-profit companies don't call me anymore.)

If you are calling after-hours, you can go through an automated system to remove yourself. You just have to press 2 and the recorded voice says your number has been logged and the remove request will be processed within 72 hours.

They're a solicitation company hired by non-profits which calls people who have expressed an interest in, or volunteered for, the non-profit.
So they say. I called them back.
I support a lot of non-profits, and am on the do not call list, so I believe them.

Left no message, by the way.

I got a call from this number a few hours ago. I didn't answer the phone, but it came up as unnamed.

The caller said my name and hung up. I don't know how they knew my name or who it was. They left no message.

Caller ID said, "Unknown Caller"

I am on the "do not call" list.

Left no message.