When someone suggests to the IRS that you might have taxable income, the IRS will inform you that you need to file a return or otherwise pay your taxes.
When the IRS get serious about you, the way they do it is to file a complaint against you. They would take it to a court, except that they have been granted blanket court action ability, so that it is like they have taken you to court already.
The way to respond is to write letters to them demanding their information upon which they made their complaint. Include a request that asks for the interest that they have in your money.
After you have all the info that they send you, file a man to man claim against them, requiring that they show how you have harmed them or damaged their property that you owe them money. When they don't provide a man that has firsthand knowledge, they lose their claim or complaint.
Usually they have already stolen property from you. Your claim needs to be for the return of your property, plus damages for your loss of time and expenses. If you don't know how to do it, or what you are doing, you will probably lose.
Listen to Karl Lentz to understand how it is done.
https://www.youtube.com/watch?v=JPGSxSStc6M
https://www.youtube.com/watch?v=wv_9vBLas5s
https://www.youtube.com/watch?v=bcs2p3veRKU
https://www.youtube.com/watch?v=_gUej6aASZg
https://www.youtube.com/watch?v=iGnqCjCwA5s
While you watch these videos, take a look at all the other Karl Lentz videos that Youtube offers. Watch any others that interest you.
Then Youtube search on "Karl Lentz common law" for even more.
Part of the point is, our government people and those running for government office are all lying to you. They can't make you liable for income-like taxes. It is against the Constitution. All they can do is offer you the option, or collect the tax indirectly through the States, or Federal corporations.