How can I turn off the firmware password on a Macbook Pro when I don't know what it is as I have never entered it?

If you don't know the firmware password, then you will need to take the laptop to an Apple Store or an Apple Authorized Service Provider along with valid proof of purchase and valid ID. I suggest contacting the Apple Store or AASP first to make sure exactly what paperwork you need to provide to them so they can unlock the Mac.

Edit: Did you turn off FindMy for this laptop? I was told that some FindMy security can also activate a firmware lock as well.

Please let us know how you make out with this repair since you were unable to remove the firmware lock. Knowing how Apple handles the firmware lock for you will help me know how to respond to other users with a similar problem.

Good luck.