ERCMPU (Milma) Not Filling The Notified Vacancies

ERCMPU (Milma), vide Notification number EU/P&A/55/2019 dated 25-10-2019 announced recruitment for multiple posts including Assistant Marketing Officer (AMO-6 vacancies notified). The final rank list with validity of 2 years was published on 08-09-2020. The first 6 rank holders were given Appointment orders and 5 of them joined by 21-09-2020. The 1st rank holder requested for extension of joining date which was given but he did not join and his candidature was cancelled resulting in a vacancy to be filled by the next rank holder which is me. As vacancy remained unfilled I contacted the ERCMPU office multiple times was asked to wait, finally on 25-02-2021, they gave explanation that as per the new Staff pattern issued by Govt in November 2020 the number of posts for AMO has been reduced to 5. All the info in public domain, notification, call letter for GD & Interview, the rank list everything mentioned 6 vacancies. What are the legal options available to me to in this scenario?