amendment in salary structure

I applied for the post of assistant scientist in PAU ludhiana in June 2014. I was called for an interview on 29 December, 2014 and got selected for the post and an appointment letter was issued to me on 29 December, 2014 with some terms and conditions (pay band 15600-37100+6000GP+100%DA etc). I accepted the terms and conditions of the university on 7 January 2015 and submit my joining report on 6 Feb, 2015 (its university rule that one cannot join the duty before police verification or one month after acceptance of offer - whatsoever happen earlier). After this, i resigned from my previous post of Assistant Professor (in another institute) with the same pay band. In march, punjab govt retrospectively amend service law for direct recruited posts and according to new rules the employee now will get only basic pay (15600), no DA, no HRA etc after 15 janusry 2015. If i had been informed about these amendments, i would not have been resigned from my previous post where i was getting the full benefits of pay (15600+6000GP+100%DA etc). Since i had not applied through proper channel, so i also scarified my previous job experience. Will these new rules be applicable to me? Can i challenge it in the court?