You most likely have a rat (remote administrator tool) on your computer allowing that very hacker to see everything you do and type,  and also to remote control your computer as well as using his computer to browse from your ip address.  My guess is that he grabbed your login for your email and used a reverse proxy to login and change your info and take your btc.  I would recommend checking your computer for malware and also checking your startup entries. If that doesn't get rid of the hacker,  then you probably should just reset and keep only what you need.