For the record, the IRS will send an individual a written notice FIRST, especially if you owe them money. They will do this a few times and expect you to take care of the matter at hand... if not, they will find out where you work, and dock your pay. The same for those with federal education loans. This will also show up as a ding on your credit report. Any collection agency is also NOT allowed to threaten you with arrest, a lawsuit, or the like, without first trying to contact you voice to voice (not this robotic call-center crap), and speak with you directly regarding your debt. They must also show up on caller ID and provide you the name of their company and the general business number for the organization. They must also state that they are a debt collector... not go into this "good luck" crap message like the one left on my phone. This sounds like a "zombie collector"--those supposed agencies that are trying to collect on debts that occurred decades ago.. if any.
I KNOW that I don't have anything errant with the IRS, and have had my taxes professionally done for the past twelve years--both state and federal. My credit score is in the upper 700s with Equifax, Experian, and Transunion. I monitor my credit reports like a hawk.
Rule of thumb: Do not pick up the phone if you do not recognize the number. If it's important, whoever it is will leave a message. When you get calls from questionable callers, especially those who leave auto/robotic voicemail, just block the number.