Dear Debalina,
I would like to tell you that there are many Colleges which offers PhD in law.
Following colleges in West Bengal offers PhD in law

1. The West Bengal National University of Juridical Sciences
2. JIS University
3. University of Burdwan,
4. University of Calcutta
5. Cooch Behar Panchanan Barma University
6. University of Gour Banga

You can check out their Official website for more information.

i hope this information helps you

All the best