Special Employment Bond

I was working in a central public sector undertaking. I applied for a sabbatical under the study leave policy on Dec 4, 2018, for the period from April 10, 2019, to April 9, 2020. As per the prevalent policy, I was supposed to sign a bond but the bond will not be applicable if I resigned during the sabbatical period. I received a letter granting me study leave on March 18, 2019 (after 134 days). But two days before sanctioning my policy, the organisation amended the policy and made the bond enforceable immediately when I proceeded on study leave. However, the new policy was not made available to me nor circulated across the organisation ( barring a select few) when my application was sanctioned. I resigned from the organisation but now it is trying to enforce the bond. I need release from my organisation before joining another and my organisation is not willing to release me if I do not pay the bond amount. Please advise.