IrinaManu wrote:
Hello! I forgot the PIN from my one IPhone which is also validated on Apple.com and visible in Find my phone...
It sounds like you're talking about a passcode you set up using Find My iPhone's Lost Mode, as this is the only iPhone passcode that has any visibility from Find My iPhone. (There is no device-specific PIN or passcode visible from apple.com.)
So you would need to turn off Lost Mode as directed here to re-access your device.