If it is not too late my arse would be down that school pleading with your teacher to overturn the decision to kick you off the course. Explain your career plans and include evidence such as ATC membership, flying experience and any other relevant stuff which will demonstrate your commitment. My thoughts are that one slip up should not equate to termination however, if your coursework thus far has been poor due to lack of effort on your part then you cannot really do any more than pledge a renewed and sustained effort should they grant you a replacement.
Lack of A-Level maths will not exclude you from obtaining a commercial pilot licence through self sponsorship (the level of maths involved is only GCSE level) however if you're looking into an RAF scholarship or sponsored commercial route then you need to get that A-Level maths otherwise face inevitable early rejection in the application processes.
Speak to your parents, teacher and then headmaster ASAP.
VFE.