I have no idea who it is. It left a voice message without calling. Indicating it is something related to my revenue, but intimidating mw that they will take action to against me if I don't reply. I certainly did not respond at all.

Robotic Voicemail from IRS saying to return the call or face penalties. I called the number back, the same robo voice said the number wasn't taking any calls at the time and to leave a message, but then that the mailbox was full.  

This is an overseas scam and not the IRS. The IRS does not contact people over the phone.

This is a Pakistan or India based IRS scam. Do not fall for it. The IRS does not initiate any legal action via phone.  
Read http://www.treasury.gov/tigta/press/press_tigta-2014-03.htm

As general background information, here are a few things you can do:

1) Report it to TIGTA under http://www.treasury.gov/tigta/contact_report_scam.shtml especially if you have become a victim (lost money, gave personal information etc.). You can also file a complaint with the Federal Trade Commission at ftc.gov/complaint (include “IRS Telephone Scam" in your complaint). This way you can also help the government establish specific fraud patterns.

2) Help kill their phone lines but not by calling them back directly (the number may be spoofed and repeat calls by you may - under exceptional circumstances - amount to harassment). The scammers use Voice over IP lines (e.g. magicJack (Ymax corporation)) to make it seem as if they are calling from the US. This is always against these companys' terms of service and can lead to immediate termination of their contract and blocking of their IP addresses for future attempts to register. Do a reverse look up of their telephone number (e.g. www.whitepages.com) to identify the Voice over IP provider and report it to the company and/or law enforcement (local police and/or state attorney general)

3) If you are really annoyed: call or write to your representative in Congress. As these scams happen all over the country maybe this will trigger a reaction and provide US law enforcement agencies with the political backing and the resources they need to work in India and Pakistan together with local authorities (it can happen, read: http://m.ndtv.com/article/india/ex-call-centr ... mmission-320427). A US task force has already been set up in Jamaica to nab scammers there (see http://www.ice.gov/doclib/news/library/reports/cornerstone/cornerstone7-1.pdf). You can use the following template for your letter (more powerful!) or email:

http://800notes.com/forum/ta-a9526ebadc65cf9/ ... 558497927242748

I got call from this number saying that they are attorney revenue from the IRS saying that they filled sue against me and asking me if I'm having lower