The aim behind reports or research that students are asked to prepare is to train them in researching and to test their abilities in doing so, and to get them used to referring to references and so on. So the students themselves must do it, and it is not permissible to prepare these reports for them, in return for payment or otherwise, because that is deceiving and lying and corrupting the new generation, and graduating weak students who cannot deal with the references properly.
It is permissible for a student to benefit from the research of others, and to take things from the internet or ask for help from some of his classmates, in some minor issues, which is something that applies to all those who are involved in research. But as for taking a complete report from someone else, this is deceit and cheating, whether he takes it from another student or from the internet, and the professor who approves of that or encourages it is partaking in the sin.
See also the answer to question no. 95893.
You have done well to stop writing reports for students, and we ask Allaah to forgive what has happened in the past and to reward you and bless you with an abundant, halaal income.
And Allaah knows best.