Calls three times each day, Never leaves a message. There is just a momentary
heavy breathing sound and they disconnect.

I have received several calls from this number (305-901-4690, Marathon,FL) as it shows up on caller ID.  No messages were left.  I have done a reverse phone number lookup and it says the number is invalid.  I looked the number up on several differrent sites and they all say the same thing 'INVALID' number.

this number keeps calling my home, every time not leaving a message. I blocked my number for a second and called the number back. It rings several time then a recording comes on stating "we apologize but agents are taking other calls.
It is very annoying, something needs to be done with phone carriers to be better filter these types of numbers

>> something needs to be done with phone carriers to be better filter these types of numbers <<

Why don't YOU filter those unwanted calls, instead of relying on somebody else to do it for you?
Simply get a phone number blocking service, app or device.
See how other 800notes visitors solved their problems by visiting this site:
http://phonehelp.2truth.com/
(That site also has a link to Amazon's phone blocker devices and apps, as well as a page showing various government sites that accept complaints or warn about scams.)

I have been getting multiple calls from (305) 901-4690 MARATHON, FL and (321) 215-4771 MELBOURNE, FL.
They never leave a message, just call and interrupt me.  
I called both back just today, 4/1/2014, and the recording was the exact same message in both cases.
"All of our agents are busy, crap, leave a message...etc...."