That 6th form person sounds stressed and unprofessional and someone was kind of like that to me too but I forgave her. I haven't talked to her since though.
Anyway, if you're struggling to the point where you can't do your homework, you could benefit from some extra tuition. Make sure to get a good tutor and do your homework the minute you get it so the work is fresh in your head.
And don't worry, you have a second teacher here:
http://www.examsolutions.net/a-level-maths/edexcel/I don't know your circumstances so I don't want to impose, but dreams betray many, but hard work is some consolation at least, even if you don't achieve your dreams. What I'm saying is, there is nearly always a way around something. You have to be dedicated and disciplined. My problem was and slightly still is: "Self-control" and I lacked the self-discipline and self-awareness to control myself. My lack of control led me to countless problems which I shan't speak of. But yeah... I thought I realised my mistakes at GCSE, but I never did. Only after the disappointment after AS exams, did I realise my utterly dark mistakes.
My last biggest issue was not knowing how to teach myself how to learn. I didn't know how to learn or study. So I had to teach myself. Indeed, it's hard work but you have to utilise many methods - Flash Cards, Routine studying, sleep, exercise, healthy eating, powerpoints, mind maps, colours, consolidation of notes every day (that means re-writing your notes and reorganising them in a useful way). I'm consistent on telling you about the guide to smash your A-levels because not studying smartly (and hard, don't get me wrong haha!) was something that let me down.