Maybe you haven't added your phone number and device to your Mi account. Check if your number and device show up in your Mi account management. Then go to Mi Unlock Status in developer options and authorize both.
If you never had a countdown, you could try registering a new account with your phone number on your phone, then go to Mi Unlock Status and authorize your phone and SIM combo.
Oh, and also enable "OEM Unlock" in developer options as well, if you haven't already.