Have an EFI lock when trying to boot in Command R

You will need to take the Mac to an Apple Store or an Apple Authorized Service Provider to have them unlock it for you. You will need to provide valid proof of purchase which usually requires your name and system serial number plus a photo ID. It is best to contact them first to confirm exactly what paper work is acceptable for proof of purchase and identity.

I think only Apple can cure that if you have proof of purchase, but...

If you have FileVault turned on, you have two additional options to reset your user password. You can wait up to a minute on the user login screen for a prompt to show up that instructs you to press the power button to restart the Mac into Recovery mode. Follow the instructions to restart your computer, after which you should see a Reset Password window show up. 

The other option is to use the Recovery Key that you should have written down when you enabled FileVault. Let's be honest, most of us don't do that, but if you did you can enter the recovery key when asked after three failed login attempts. Be sure to use upper case letters and to enter the hyphens -- they're required. 

Any method we outlined is an effective way of regaining access to your account, or if your child forgot their password. Of course, if you can use this to get into your Mac, so can someone else who has access to your computer. You can prevent that from happening, you'll just need to be more proactive during setup with storing recovery keys and remembering your password. Here's how to lock down your Mac.

https://www.cnet.com/how-to/you-forgot-your-macs-password-heres-how-to-get-back-into-your-locked-down-computer/#:~:text=With%20your%20Mac%20turned%20off,up%20below%20the%20Apple%20logo.