Once follow my instructions
Open mi cloud website and check how many devices are showing connected if there are any other devices showing connected and offline please remove them.
Now open your device and turnoff find device and logout your mi account from your device.
Now reboot device and login to mi account using your registered mobile number and turn on find device and sync the device perfectly.
Now turn on usb debugging and add account in mi unlock status if you have added already please ignore.
Now try to unlock bootloader and see if it is getting done are not if now and showing 168 hours then wait 168 hours again and during this waiting period please don't signout your current mi account if you do that the waiting hours will reset to 168 again no matter what.