The IRS does NOT call you. They either send you a letter, or they appear in person, and show you an ID card.
The IRS does NOT have to file a lawsuit. They are an administrative agency. They tell you how much they think that you owe, and you either pay it or you don't. After that, they can seek administrative remedies, without going to court.
Did they threaten to have you arrested? The IRS doesn’t do that either. It's an administrative agency.
Are they going to send a sheriff to serve you papers? "Sheriff" is not a Federal position.