For the MCA course its required to have Mathematics in your UG level and for most of the univeristies you need to qualify the entrance. So if you have the pure Mathematics course in your BCOM UG program, then you are eligible for the course of MCA but if not, then you can't do MCA after your BCOM.

For more information regarding the MCA courses consider the link provided below:

https://www.careers360.com/courses/mca-master-of-computer-applications

I hope this helps. Wish you a great eve!