Bootcamp - Bootcamp could not locate OS X volume

Hey, I’m in a bit of a pickle here that I can’t quite figure out how to fix. Right now, I’m running bootcamp on Mojave (I am so sorry, I don’t remember the exact version) and whenever I try to switch to Mac OS X it doesn’t let me. I’ve tried the restart option/alt however it brings me to a firmware password and I don’t remember setting one at all. I’ve tried every single password that I’ve written down and no dice.

I brought it to the Apple Store and they said they couldn’t do anything without a receipt proving that I purchased the Mac, which I no longer have since it’s been 3 years. I’m really at a loss here and I don’t know what to do. Please... please help. I need to be able to switch between Windows and Mac OS.

(I can’t do a hard reboot either because I have a lot of important files that if I lost I would probably have a breakdown) (BY THE WAY... I’m in Windows atm, so recovery mode isn’t working.)

Hopefully you guys can help. I’m really desperate.