they never leave a message.

Hangs up as soon as I answer.

Call from Kurt at Traders International. Some kind of investment thing.

This number calls and never says anything.  For sure a collection agency, but must be for a bill that is years old.

Got a call, heard background noise (people talking). Got no response. I called back and got the same message everyone else is getting.

Called them back and said "thanks for calling the administration office." Any company with that vague greeting is up to no good.  Most likely a collection agency.

called but left no message. I called back and it said thank you for calling the administration office.  please leave a message and someone will get back to you.