Is it possible to get back the refund from IISWBM KOLKATA after getting the admission ?
Nope, you won't get refund if admission process is completed. You can get refund only when the purpose of the process is not fulfilled. as you said, you have already taken admission which means purpose of counselling process is completed.
you won't get refund now. for more information, please visit the help desk of the institute @ http://www.iiswbm.edu/
Hope it helps!