I’m gonna ask some annoying questions sorry, I can’t promise that I will be able to solve this but let’s give it a try.
Do you have any ide about how you got hacked? Did your “friend” have physical access to your phone or did you install anything this person sent you? Do you use any web applications connect to your phone apps like whatsap web, telegram or similar where you can read your messages on your computer?
Could you check if any apps drain more power (battery) than usual? Any app despite how harmless you think it is.
Could you install a network monitor like glasswire or a similar app to see if any app uses more bandwidth then usual? You could also try something like an app called network connections to list what ip addresses specific apps talk to.
Like Emile stated above. Don’t panic the harm is already done. Oh and by the way make sure to save all or any proof that your “friend” sends you about this on a cold storage (not your phone) It can be useful later on.
change your passwords everywhere from another device and do not sign back in again until you are in the clear. Even if it’s a “friend” at the moment this person could turn against you at any time, don’t make it easy.