You should have evidence to prove that the company did not produce or use the product protected by the patent before the date of your patent application. (Is your investigation provable?) You can ask him to produce evidence that was produced before the filing date, but you as the plaintiff (if suing) have the burden of proof. If you can prove it, you can request the local patent management department (the provincial Intellectual Property Office) to handle it. Of course, it is also possible to file a lawsuit directly with the People's Court without going through the patent management agency.
Three exams only!