How to convince school to let me retake my subjects in year 12

Hello

I want to retake my subjects in year 12 as I'm in year 13. I've had a lot of horrible things going on during year 12. My school is letting me retake year 12 but not the subjects I want due to my previous bad grades. At first they called me in and said I can retake year 12 just not with my subjects. I was devastated but I didn't want to give up. I wrote a long email giving my school all my thoughts and some of what was going on. I poured my heart into that email. But in school all they said was nice email but sorry we won't. I accepted it as I find it difficult to speak my mind face to face. But then a day later they were forcing other subjects down my throat and I had to amp myself up and ask them if I can do like a trial thing and you can look at my grades regularly. They shut me down so quickly. They said they don't want to risk it and that they won't think about it at all and that UCAS points is better than no UCAS points no matter the subject. But I just know I can do well. I've planned it all out. I know how to do better. So now I'm stuck. I have to make my subject decision on Monday as it's already been almost 2 weeks since the year 12s have started their subjects. I was thinking about like memorising some speech or something that I can say to him to convice him. I'm out of ideas. Please help. I don't think I can move schools because this is the only decent school in my area and it's an hour away on the bus. And if I move my brother in year 7 will have to too. Do you know how I can convince him? If the speech thing is okay then what points can I make and what persuasive things can I use? I've been stressing about this for 2 weeks I can't get any sleep I have chest pains when I think about it. This is my future and I know I can do well this time.

Thank you for reading this