need helping finding ip address from a whatsapp phone number or other services like it

my wife has has a stalker for 4 years continuously making new phone numbers and she cant change the number because its for work. she works in the adult entertainment industry and this person is trying to ruin her life, and im fed up. he has been making fake reviews and fake appointments. im trying to find a way to get this persons ip address, possibly block it from sending msgs of any kind from any fake number service. i really dont know what my options are. if anyone can help i would appreciate it.