A levels subject

This is long but I need help, I got a B in English lit, E in economics and a U in maths for as level our school requirements to carry on is u have to get a D, E is a low pass and a U is a fail, I am willing to change my maths subject for an as but economics was the first time I did so bad my predicted was a C. However there were students who got the chance who’ve “failed” to continue their a levels I got an E but I was told I’m not doing econ while someone in my old econ class FAILED and still are doing it which doesn’t make sense to me at all it felt unfair in that situation. I go back the next day before I could speak to my head of yr she was fuming her face and tone entirely dropped she was on the verge of shouting but held it back but she kept throwing in my face “never doing economics” I can’t tell what to do now I really use to enjoy studying econ and wanted to pursue it in uni. I’ve never been treated this rudely by a teacher that’s supposed to support me she complained having to sit two hours with me to “help” me which she barely did she Answered a few questions here and there the other times she’s gone or on her phone or talking to someone while I was selling advice accs help from my cousins???