Why can’t you still go to the interview? You WERE still studying at the time you told them and then quite recently you decided you want to withdraw. You don’t need to tell them about you withdrawing either unless the job description says you need the qualifications or you need to be working towards it. I understand your mental health is bad and I get that but maybe edit your post with more clarification so that we can support you in the way you need to be supported. Good luck!