B.Com

Dear Anup,
For UPSC, one must know, "What not to study". Start preparing for current affairs from now onwards as it will become past till the time you get ready to appear for the exam. Keep your knowledge updated about everything that is happening near you, nationally and internationally. One should be able to speak on any topic reflecting that one knows about it. Carefully revise general studies as it will be with you if you are in the regular practice of reading it. Keep thorough and in-depth knowledge of your stream of graduation. Read as many news papers and books as you can. Reading itself will develop a new and confident personality of yours.
I hope this would suffice. All the best and god bless you.

Yes, you can pursue M.Com.
Some colleges in Kolkata are:
1) University of Calcutta
2) Goenka College of Commerce and Business Administration
3) The Bhawanipur Educational Society College
4) Shri Shikshayatan College
5) Ananda Mohan College
6) Scottish Church College
7) Prafulla Chandra College
8) Asutosh College
9) Bhairab Ganguly College
10) Derozio Memorial College
I will suggest you that with M.Com do some certificate course which can help you in developing your skills such as
1) Tally
2) Certificate course on forensic investigation
3) NCFM ( NSE certification in financial markets)
4) SAP FICO
5) Certificate course on EXIM
6) Digital Marketing
Else, prepare for banking exams, insolvency professional exams. And if you are thinking about earning while learning and want to seek practical knowledge then go for internship in the field you are interested in. Moreover, it will help you in identifying your interest in a particular branch/ field.
All the best.