I had an admission in idol university for the year 16-17 for fybcom..but didn't gave the exam
Are you asking for Institute of Distance and Open Learning, University of Mumbai? As per the official the students who enrolled in IDOL before the academic year 2017-18, have to register Fresh to proceed with the admission process. I would suggest you to contact the official with the given below contact detail to get it clear.
http://archive.mu.ac.in/myweb_test/contact_us.htm
Good Luck!