Over qualification Regarding

I have passed my diploma in Mechanical Engineering with First class during 2000. After this I have tried for lot of Govt. jobs and attended various interviews including BHEL (2 times). Later in 2007 I have joined for B.Tech in Mechanical Engineering and successfully completed in 2011. Then I joined for a private job. As per my Employment Exchange registration I have called for a written test and shortlisted for interview at Bharath Petroleum Corporation Ltd on Nov. 26th 2014. for the post of General Workman B(Mechanical). The basic qualification for the post was Diploma in Mechanical Engineering with First class. In the call letter they specified the Qualification as "You possess First Class Diploma in Mechanical Engineering (Full time course) with 60% marks or above (BOTH FIRST CLASS AND 60% MARKS COMPULSORY). (60% marks is relaxed to 50% for Scheduled Caste/Scheduled Tribe & Hearing/Orthopedically Handicapped candidates.) {Candidates having Diploma in Engineering in any other discipline viz., Mechanical (Production), Mechanical (Tool & Die Engg.), Mechanical (Medical Lab), Mechanical (Maintenance), Mechanical (Automobile), Mechanical (Foundry Tech), etc., and any other Diploma in Engineering equivalent to Diploma in Mechanical Engineering are not eligible for consideration. Engineering Graduates including AMIE holders are also not eligible for consideration". I meant it as "Engineering Degree and other Diplomas in various disciplines in place of Diploma in Mechanical Engineering is not eligible for consideration. So I gone for the written test and marked as "YES" for the a question - " Are you passed Engineering Degree" in the hall ticket and return to them. Later they called me for the interview, and I have reported for the interview. During the verification they asked me "Do you have Engineering Degree?" I replied "YES I have both Diploma in Mechanical Engineering and Degree " , Then they told "sorry you are not Eligible, we need only Mechanical Engineering Diploma holders". I argued, "I have diploma and I don't want any special consideration for degree in future, you can consider me for Graduate posts as a fresher." But they don't consider my case. sir, I came to know that in BPCL there are special quota for Engineer posts for the BPCL staff they hold Diploma level post and having Engineering Degree by considering there service and and performance. Since the fact is like that, why they deny my candidature. I think higher qualification will be good for the company in most of the cases. As it is a Public Sector Company, the company official have any right to implement such rules ? Sir, a) Is they have any right to say like that? b) As an Indian Citizen I think, it is my right to acquire any Education and Degrees. Is it right sir? (I am studied by spending my own family money). They only want to insist in the basic qualification since these are all Professional qualifications. c) Can they deny my candidature only because of my Engineering Degree? I have the basic qualification, If they don't want my degree they only can deny me from availing any benefits for it. Why they can completely avoid me? d) Is there any provision to impose such rules in a public sector company? e) There is any court order or verdict relating to such matter? In the above said matter I need an urgent legal advice since the interviews are going on. Thanking you sir, Expecting your valuable reply. yours Truly, Sakkeer Kalliyath