Undermined Female Teacher

Over the last few months, I’ve been teaching English to business professionals in my city. I have An Honours BA in English literature (distinction) and a Master’s in English from a top U.K. university and some of the men I teach STILL try to undermine me in class. One student continuously challenges me on grammar, pronunciation, etc when he can barely speak English. I get so angry and hurt, I don’t even know how to react. I can’t help but feel he does this because I am a young woman telling him that he is wrong and he cannot admit to not really knowing anything. Another student questioned my nationality (assuming I was Canadian) because I wasn’t familiar with ONE idiomatic expression he just happened to hear. I have two degrees in english, I am a freelance writer and I am sick and tired of men thinking they know everything when i’m an expert in my field.