Help ASAP

Basically, I went to a new school to enroll and was told a few months ago I could do Maths, Further Maths, Biology and Economics. When I got there, they said I could do Maths and Biology but Economics and FM clashed. I then chose to do Business instead of Economics.

I was then told after being accepted on to the Biology course that I couldn't do it due to the fact I got Cs in 21st century Science (long, long story :l) so I got stuck doing Classical Civilisation.

My sister who goes to my old school tried to get me on the Biology course at my old school (previously said I couldn't do Chemistry and Biology together but never separate). My neighbor, who happens to be the head of 6th form for my old school, came and said they wouldn't let me do Biology but I can do Maths, FM, Geography and Psychology.

I'm still able to beg to be able to do the biology at my new school but it's unlikely. What are my options at the moment? Could I resit/re-do my Science GCSE? I just don't want to get stuck doing options I don't want to do and although I did poor at GCSE in Science (Again, long story), I know I'd be able to do well should I apply myself unlike the others.