Macbook Pro Hacked

Hi,

My MacBook Pro was hacked by a former flatmate a month ago. The person had access to my MacBook for multiple hours on daily basis and iPhone (iPhone daily less than an hour at a time as I showered). I moved out of the flat the day after finding out (though this was likely several weeks after it was first hacked). In addition to resetting the passwords to all my accounts, I reset my MacBook and iPhone back to factory settings and downloaded the respective backups multiple times since then. However, I believe they may still have access to my system. Could someone help me out with this?