You can't cancel your exam now. You will either have to attend it give it a go or simply not turn up. You cannot get any money back now as it is too late.
You had until 26 October to have done so, I'm sorry:(. Unless if it happens you sick on the exam day.
ALTERATION ON EXAM ENTRY CLOSES ON THE LAST DAY OF STANDARD ENTRY. SO AS OF NOW IT IS TOO LATE BECAUSE THE STANDARD ENTRY FOR DECEMBER 2015 CLOSES OCTOBER 26,2015, AND THAT IS PAST ALREADY.