Disparity in Pay upgradation

Hi dear laywers I'm working in government research institute autonomous body for the past 6 years from 2016 to 2022 till date I have selected for the post of Lab Technician in 2016 during that time recruitment rules for that post is DMLT/ BSc MLT/BSc lifescience. With gradepay 2400gp I was completed my DMLT with BSc lifescience before recruitment process and I was selected for the job with this qualifications only with direct recruitment I was selected by meritorious basis During 2020 suddenly govt changed Recruitment Rules and grade pay as education qualifications BSc MLT only and grade pay 4200gp without asking stakeholders comments and they promoted new rules that if lab technician want 4200gp he/she must possess education qualifications as BSc MLT only then only they will get pay upgradation This is my question how to get this pay without doing that stipulated qualifications Is there any rules available for saving clause of incumbents How to get this grade from this pay disparity among same cadre getting different pay while doing same nature of duties in same nature of work kindly let me know the law details and rules for my current situation thanks and regards.