Information from a French mobile number

Hello (sorry for posting here, I didn’t find a corresponding category.) I would like to know if there is a way to obtain information from a French mobile number. A member of my family received a message from a stalker describing her washing dogs in the garden (which he really was doing) and threatened him. Given the nature of the French police, I would like to take the lead in recovering evidence. I have just 2 months of practice in pentesting and have not yet gone beyond the easy level on the tryhackme boxes. Thanks you.