I can't pass GCSE Maths!

Okay so firstly, I'm in year 12 of sixth form and I'm not an awfully stupid kid; in my GCSE's I got mainly A's and B's. I'm doing my A Levels now however i have one problem. I still can't pass my Maths GCSE. In year 11 (my first time doing a maths GCSE) I got a D, 1 mark off a C. i sent it off for a remark however it came back exactly the same. This was a foundation paper. I did the resit in November and
i got the results a couple of weeks ago and this time i got an E! That time I also sat the foundation paper. My next resit is in summer (so i have lots of time to revise) and i will also be sitting for the higher paper because i have been told it is easier to pass than foundation. The teacher i have now for maths isn't very helpful at all so i was wondering if there are any websites or revision guides which can help me pass. I'm desperate to pass this time because it is an essential subject for me getting into university and i would rather pass it sooner than have to keep redoing it whilst I'm in year 13 when the work is getting predominantly harder and my focus will need to be on my A Levels.