See as per the UGC guidelines, the duration of completing the BCOM degree at maximum is 5 years from the year of registration. So if you have your registration from 2013 then you would have been eligible to be again appear for the examination of semester 4,5,6 till 2018. As the time period had lapsed, it may occur you can't take admission in the previous case but you can obviously take admission as a fresh student in 1st year of BCOM.

Although to be sure, you should contact your college/University if the rule & regulation varies, but in most cases, if your university is UGC recognized then you won't be able to appear for the examination. Still you should contact to be sure!

All the best!