If the clog is deep or stubborn, a plunger may not reach it. A toilet auger (or closet snake) is a tool designed to hook and break up or retrieve obstructions.
If you don’t want to buy one, call a plumber. Do not keep flushing—that will only flood your bathroom floor. how to unclog a toilet filled with poop
You need a flange plunger (one with a soft rubber flap extending from the cup), as this is designed specifically for toilets. If the clog is deep or stubborn, a plunger may not reach it