Professors who don’t admit they are wrong

Have you ever had a really bad professor? One of mine made up her own rules about significant figures. Apparently 200 without a decimal has three significant figures. I even sent her the textbook rules from the prerequisite courses and she told me "not all sources are authentic". She's literally trying to gaslight me into thinking I don't understand significant figures. Her question about the number of sig figs on the MT was FOUR (4) POINTS and everyone who answered the RIGHT ANSWER lost FOUR (4) POINTS. What do you even say to someone who absolutely under no circumstances will admit they are wrong