how do do you stop your phone from being hacked?

I know someone that started taking cyber-security.  ever since then I keep being hacked on my phone.  can anyone tell me what to do?  Have reset my phone 3 times loosing important information everytime.  Its frustrating because I think this person also hack my internet.  I have changed phones and that person was able to hack my prepaid phone as well.  I hope you can help this is getting ridiculous.  I also notice an account that I know is the hackers under the reset tab.  If I give it to tmobile do you think they can trace it and stop the hacking? Have gotten in my google emails and in my 2 step verification have greyed out the send a text option. that person also greyed out me changing my password on my internet service.