How is he targeting you? Is your system pawned ?
1. First format your system and install any antivirus software ( assuming you on windows ).
2. Reset factory settings on mobile
3. Get new mobile number if it is easy
4. Change password of all accounts.
5. Enable 2 factor authentication whenever possible. This will help you for sure. Keep backup codes somewhere safe(may be flash drive or print them). In case u lose access to your phone/number those will come handy.( Don't delete accounts suddenly. Just Change passwords and enable 2 factor authentication ) So no one can impersonate you easily and you will come to know if anybody has accessed your account.)
6. Don't click on any link in web foolishly. If there is any link just hover your mouse on it, it will show you address in bottom. If address looks suspicious, don't open link.
7. Don't click on any link in your email. When you get any email alway check from what email address it came before clicking on link.
8. Don't log in important accounts on public cafes, library computers etc. Access them from your system only.
9. Also look for hardware keylogger device if you too paranoid
These points are not 100 % full proof. But none the less they will help you for sure. Remember hacking is not magic. You can not be hacked suddenly from nowhere. Always be vigilant.
