Noc issue

Hi, I am working in one of the PSU. I have joined the current PSU on the basis of my previous experience in private sector in year 2006, as one of the eligibility criteria that time. Then after i passed many departmental exams. In year 2013, PSU has notified vacancy of post "X" for which internally i was in "Y" where "Y" is the feeder grade of "X". As per notified eligibility criteria, the requirement was not fulfilled by me, as they were not ready to consider me as internally despite of representation. Since their intentions from day one was not to allow internal employees...Somehow they not able to stop me being my experience private+govt. fitted into their eligibility criteria..i have applied from outside thru proper channel.......but when interview committee has done the selection they again shown their malafied intention and placed me in waiting list...and when it was finalized that main list selected candidates are not joining, then after they have not cleared the waiting list and took one year to clear the waiting list after my seven representations. After my struggle finally in year 2014 they gave me post "Y" till that time i completed my one and half year on post "X". Now in year 2015 and 2016 for a post "Z" for which "X" and "Y" both are feeder grade, they hold departmental promotion exam and made me eligible both times. The eligibility criteria was 5 years regular service and one year minimum in "X" and date of experience eligibility as on 01.01.2016. The Promotional ladder is i.e. X(Feeder Grade with three years service)>Y(Feeder Grade with three year service)>Z. Now come to issue: I have applied for NOC for applying in another PSU for job as equivalent to ""Z" in my current PSU. Now my PSU has refused to give me NOC basis reasoning that since i am a fresh recruit in year 2014, hence as per company policy without completion of three years they will not allow the application forward... Now my contention is, if i am a new recruit then why i was allowed to sit in the departmental promotion exam by including my service before 2014 as well, because other co-recruitees were refused to sit in that exam basis they were not having company five years service. The numerical presentation i.e. 2006(initial Joining)>2013 (Joined in X)> 2013 (Selected for Y's Waiting list)>2014 (cleared the waiting list)> 2015(appeared in First departmental promotion exam with five year regular service eligibility criteria)>2016 (Appeared in Second departmental promotion exam with five year regular service eligibility criteria)>2016 Applying NOC(Refused NOC basis non completion of three years service in company) Now advise what should i do...