Ashutosh Neogi (Service) 25 January 2019
Since your job offer letter is a civil contract, the terms and conditions of your offer letter and /or apointmentment /engagement letter is the final source to get your answer.
If such documents are silent, then you may raise an application for refund of your security deposit. You may mail or submit hard copy of application with acknowledgement request.
You are not clear what documents you have in support of your security deposit made by you. If any such documents available,it is advisable to refer the same in your application and submit a copy of such documents with application.