company not returning original marksheet

Hi i am from lucknow. I started working in a company and they deposited my original marksheet and gave me a xerox copy of it when written notice on that xerox of service bond of 2 years. That was not a legal service bond it was just my marksheet's xerox copy on which they wrote and we both signed. But due to some reason i resigned after only 2 months. Now they are not giving me my marksheet back. What should i do as they had not given me any legal stamp bond. It was only xerox copy of my marksheet.