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You might be able to get out of it by reading their own laws and learning to read through the sneakiness. Personally, I wouldn't pay anything yet, otherwise you have validated the debt and then you HAVE to pay it. Quick note: 26 USC 6065 says that for their 'bills' to be valid, they must sign it under penalty of perjury. Do they do that? NOPE. Because no agent is going to stick his/her neck out for that.
26 USC 7701(a)(1): The term "person" shall be construed to mean and include an individual, a trust, estate partnership, association, company or corporation.
Reading this through the lens of ejusdem generis which is a part of statutory construction, the term 'individual' must be in the same class as the other terms listed, which are commercial entities. i.e. not a man/woman
26 USC 7701(a)(14): The term "taxpayer" means any PERSON subject to any internal revenue tax.
As we saw above, you are not included in that definition of person.
26 CFR 1.441-1(b)(8): Taxpayer has the same meaning as the term PERSON as defined in section 7701(a)(1) (e.g., an individual, trust, estate, partnership, association, or corporation) rather than the meaning of the term taxpayer as defined in section 7701(a)(14) (any person subject to tax).
Self explanatory.
26 USC 7343: The term “person” as used in this chapter includes an officer or employee of a corporation, or a member or employee of a partnership, who as such officer, employee, or member is under a duty to perform the act in respect of which the violation occurs.
Self explanatory.
As in the link above, sometimes all it takes is reading the tax code and sending them a letter for them to realize, "Oh shit. This isn't a regular monkey I'm dealing with." And get yourself no tax liability because YOU ARE NOT A TAXPAYER as you just saw from their own definitions.
If you send them letters, KEEP COPIES OF EVERYTHING, send it certified mail, return receipt. This isn't hard, but people have been brainwashed into believing that the IRS has tons of power because you only ever hear about idiots who just stop paying altogether without knowing what they're doing.
If all of the above is not something you're willing to do, you could try to do their "Offer in compromise" which is one of their forms to try to get them to let you settle the debt for less, but it's up to them. Using this form is continuing their presumption of your taxpayer status.
There is also the possibility of using "accord and satisfaction". Once the debt is disputed, if you don't their responses (or their potential counteroffer when you write a letter), you can send them a check for a lower amount with verbiage on the memo along the lines of "full and final settlement" and on the back, under the signature line, along the lines of "by cashing this check you agree to full discharge of obligation on account number XXXXX". If they cash the check and don't refund it within 90 days, that becomes a "renegotiated contract" and if they were to try to come after you for the rest of the debt, you would be able to sue them for breach of contract.
See the below case to get a better understanding:
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