I am very sorry to learn you're receiving such calls! Have you reported them to the authorities?
That said, for security and privacy reasons, incoming calls details are not displayed on the customer's invoice and it is not possible for you to trace them. If for any legal matter you need these details, you can contact the authorities and they will in turn contact us for details. Please bear in mind that they will need to provide legal documents to obtain any such information i.e. warrant, subpoena etc.
I hope everything works out for you. 🙂