Am I right not to obey my mother regarding food and benefiting from the money of haram Saudization, and what is the ruling on my current benefit from what my mother bought with this money?

We cannot definitively rule on the impermissibility of your mother's salary without details. Deceiving the work system and taking an undeserved salary is not permissible. However, if a person contracted for work, exerted effort, then the employer excused them and did not demand anything from them, and the salary was from a company and not from the state, then there is no harm in it. If you are certain, with knowledge and insight, that the money is forbidden, then your refusal to benefit from what was purchased with it is correct. But if you are not certain, or you do not have a legitimate proof, then your action is incorrect if it harms your mother, as obedience to parents is obligatory in matters of doubt according to most scholars.