If you're facing allegations that you lied as part of a conduct proceeding, be it an investigation or a hearing. In other words, you're going through the process and then additional charges are brought because the school believes you made a bad faith misrepresentation or false representation, and now you're facing new charges because of that, you have to defend against that vigorously.
It is a serious allegation. The expectation is on a student to be forthright during the course of an investigation. To lie or to be accused of lying during investigation, or as part of a conduct proceeding, can result in severe consequences. If it's a good-faith mistake or a misunderstanding as to the circumstances, and if the school is just not understanding that aspect of it, that would need to be presented at the given time.
It would have to potentially be documented by whatever evidence may be available to support the claim. You can't depend on the school to do the right thing. You have to take the necessary precautions. You have to respond appropriately. An experienced attorney advisor can be your best ally in understanding the process and navigating it moving forward. They should be involved if you're facing an allegation of that nature.