Missed call from this number

The number 314-345-2900 belongs to the United States Postal Service claims department for damaged domestic package claims. This is a positive ID as I have a claim for them and they returned my call from this number. They also left me a message to call them back on a toll free number which is a good number.
Caller: United States Postal Service
Call Type: Event Reminder

My parents got a call from this number yesterday.  "National Insurance Advocates" was displayed on the caller ID.  They did not answer.

They keep calling me also and will not leave a message and I will NOT answer the phone, so they might as well stop calling

I've been getting one call each day from 314-932-0977 (excluding weekends and holidays) for a while now on my land line.  They call any time between 9AM and 5PM.  They never leave a message.  I don't answer any unwanted calls like this.  My belief is that the only way to stop the ever-growing plague of nuisance calls is to never answer them.  Unfortunately, a lot of people must answer, because the problem is just getting worse.  The situation is way out of control!