Caller ID says "MASSACHUSETTS".  They leave a message.  Their software is too stupid to wait for the beep, so I have reconstructed the beginning of their message from previous attempts with other numbers, "Hello, this is Rachel at card holder services, calling in reference to your current credit card account.  There are no problems currently with your account.  It is urgent that you contact us concerning your eligibility for lowering your interest rate to as little as one percent.  Your eligibility expires shortly so, please, consider this your final notice.  Please, press the number “1” on your phone now to speak with a live operator and lower your interest rate, or press the number “3” to discontinue further notices.  Thank you, and have a great day." (I never go on the DNC list as it can actually make things worse).

I call back after hours (using *67 to block my number).  I hear the following, "<tone> The number you've dialed is not in service. <silence>"  The silence goes on for about 3 minutes and then it hangs up on me.  If this was some phone company message, there would be no extended silence.  I believe the statement plus the silence is their outgoing message.

So the caller fakes a disconnected phone and has a spoofed caller ID.