The Commissioner of CGST and Central Excise, Dibrugarh appealed before the Gauhati High Court against orders of the CESTAT (Kolkata) which had allowed refund claims by Oil India Limited and ONGC for Education Cess (EC) and Secondary and Higher Education Cess (SHEC) paid by mistake on Oil Industry Development (OID) Cess. The core dispute was whether the one-year limitation period under Section 11B of the Central Excise Act, 1944 barred these refund claims, and whether the statutory presumption of unjust enrichment under that section was properly addressed. The CESTAT had held, relying on decisions of several High Courts including the Gujarat High Court in ONGC Ltd. v. Union of India (2017), that since the EC and SHEC were paid under a mistake of law and were not validly 'duties of excise', Section 11B's limitation did not apply and the general limitation under the Limitation Act, 1963 (specifically Section 17) governed instead. The Gauhati High Court examined these two substantial questions of law regarding applicability of the Section 11B time-bar and the unjust enrichment presumption in cases of payments made under a mistake of law.