Don't reinstall your OS - switch to Linux. Mint is fairly close to Windows if you are not familiar with Linux.
Windows 10 includes Cortana, which cannot be removed. This is a keyboard logger ( amongst other things ), and stores all of your info and communications in the Microsoft cloud.
When I was a victim it was advised to me to change the hard-disk and when asked they said changing OS is not the permanent fix. Can you explain which one is the right.