activation after iOS 10 upgrade

Hi all,

is there a problem with iOS 10 upgrade? I restored my iPhone 6 with a downloaded version of iOS 10. I can't get access to it now because it's said that my iPhone 6, which I unboxed myself it's been 2 years, is linked to a Apple ID that I don't know nothing about. I checked the list of devices (iPad Pro, iPad Air 2, iPhone 6, iPhone 5, MacBook Pro) linked to my Apple ID and of course the iPhone 6 is on it with the same IMEI...

Has the iPhone 6 been hacked? What should I do?

I'm writing from Haiti. Help me please!