Firmware Locked Password

I have an 2012 imac with the most current Update software being High Sierra. I've seemed to have locked the firmware and I can't get passed it I don't have a receipt so no in store help. I've put "resetpassword" in terminal, I've took out the ram, I've made a bookable removable disk, I've put the original DVD that came with it and at this point I have a great looking paper weigjt. Please Help!!!