IDK what posts you were reading but almost all endodontists, after they scrape out your pulp chamber and tubules, fill them in with gutta percha, which is not amalgam.
When they do an apicoectomy and they clean out the infected root tip, they're supposed to fill it in with a biocompatible material. Your dentist thinks silver-mercury amalgam is biocompatible?
Dentists by law are required to keep records. You need to go back there, slap him in the face, grab him by the lapels and say, "LISTEN YOU MONSTER!!! WHAT F*CKING PROCEDURE DID YOU DO ON MY TOOTH?????"