The Sikkim High Court in a 2015 judgment held that distance education degrees are valid for all the students admitted on and before the date of judgment.
When the Distance Education department of UGC filed a Special Leave Petition under Article 136 of the Constitution of India, the Apex Court declined to admit the SLP on the ground that the relief granted to the students by the High Court cannot be questioned based on the facts presented to it.
The apex court said that distance education has to run at a distance and it was not correct on the part of IGNOU to stop any university from offering such courses since it is helping a large number of students. The court highlighted the fact that if foreign universities can offer their courses in India then why not PTU.
That being said, writs are the prerogatives of the High Courts and the SC to protect the legal and fundamental rights of the citizens.
Writ of mandamus, in particular, can be issued by a superior court against the inferior courts and public bodies
which have breached their constitutional, statutory or public duties.
Mandamus can be also issued against any private body as well if, for the enforcement of a public duty.
With reference to your case, IGNOU is a central university, which has ignored the SC order on the validity of a certificate of distance learning. Therefore, the SC may, through the writ of mandamus, direct the University to comply with its orders issued in the previous rulings and accept the admission forms of the students holding DE degrees.
You can approach the SC under Article 32
of the Indian Constitution which does not bar direct petitions from the citizens in case of violation of rights under Chapter III of the Constitution.
Sikkim Manipal University vs. IGNOUand Ors., WP (c) No. 04 of 2013 
Articles 32 and 226 of the Constitution of India 
D.D. BASU, SHORTER CONSTITUTION OF INDIA (1979) 553. This also includes executive orders and directions issued by the superior courts; see Union of India vs. S.V. Vohra, AIR 1967 SC 993. 
Binny Ltd. v. Sadasivan, 2005 (6) SCALE 435
Miscellaneous References: http://www.amityedumedia.com/EduNews-issue23.2.htm http://news.education4india.com/1114/supreme-court-ruling-on-distance-learning/