However, in the scene you described, although there is a problem of employing at a lower hourly wage and engaging in heavy physical labor that is inconsistent with the agreement, the key lies in your age. Because you are under the age of 16, you are not qualified as a legal subject of labor relations, whether it is handled as "child labor" or as a general labor contract dispute. Therefore, it may not be supported to report the employment of child labor directly through the labor bureau, because the labor bureau will first demand the protection of minors' right to education, rather than participating in labor.
I suggest that you reflect this situation to your parents or guardians first, and you can express your dissatisfaction and claim your rights and interests to the relevant units through them. At the same time, parents or guardians can also report the illegal behavior of enterprises to schools, communities or local government departments for help and solutions.
In addition, all units and individuals should abide by the law, respect the legitimate rights and interests of minors, and may not arrange minors to engage in labor that is incompatible with their physical and mental development.