@CR43
How did you get in this situation? That is, how did the IRS find out about the $400/month? Did your significant other (SO) claim that they paid rent in order to get some government benefit? SO can't call it rent for one purpose and you call it not rent for another (income tax) purpose.
You're probably not going to find the above rationale in the tax code. If you want to fight this, you're probably going to need professional help. Even if you give in to the IRS, you may want to have a professional prepare your amended return in order to get any available deductions.
