How do I regain control of hacked iPhone and iCloud to recover deleted WhatsApp chats

I got hacked. I tried to change the phone and iCloud and the Wi-fi, but that did not give any results. I stall notice the same problem. They could to control in all my device. Also I notice some of my WhatsApp chat got

deleted. What should I do?

[Re-Titled by Moderator]

Original Title: Remote Control