Unable to login to account
For now, you've a couple of options to fix this, but pray you'r Mac's connected to the internet.


If you've enabled 'Reset passcode with Apple ID' in System Preferences, great!    But... why this thing probably wouldn't work is---


You're Mac's disconnected from the internet (in some cases it might work)
You haven't set up iCloud on your Mac
Dang you forgot the iCloud passcode as well.

Take it to an Apple authorised service centre. You might be able to recover it if you still have the bill and warranty details of your Mac.
I've never heard of firmware passcode. Clearly, you have access to the internet so you could probably look up possible passcode (like I don't know, 000 or passcode123 or something, keep trying as long as it doesn't lock you out).
Otherwise, uhhh, there's absolutely nothing you can do. Apple devices are known for their superior encryption technology and safety. Illegal breaking in to your computer is hard, but maybe (maybe) possible. 


Hope this helps!