How do I get a hacker out of my phone?
Look through your installed app (in settings). Is there some new weird app you have never seen before and not installed yourself which is labeled as "System-App"? Yes? Your are screwed. Only way to get rid of it is to re-flash the whole ROM. Well you could also root your phone and use one of countless apps/modules to remove System-Apps. But God knows what the virus will do when it gets root access. 
I have seen this years ago on a Huawei Mate 1. The app was turning on WiFi and Data permanently to load ads and malware. Factory reset did nothing. Clean flash of a new ROM was the only way.