Calls several times a day.  Never leaves a message and can't call back

Called my cell phone.  I rejected the call.  Immediately called right back.  Rejected it again.  Then immediately called a third time.  I blocked the number but this is ridiculous.

I never answer calls from numbers I do not recognize like this one 903-780-2431. These people didn't leave a message and I don't call these numbers back. I am on the National Do Not Call list what is up with that!!!!????

I got a call from this number.  Did not answer it right away. They did not leave a message; but when I was free I called it back & a recording said it is not a working number.  That is strange; 10 minutes later it is not a working number.  So I decided to google it when I got home to the computer.

Received a call on my cell phone.  They did not leave a message.  Tried to call the number back, but got a recording saying this was not a working number