Service tax Construction of Govt school by Contractor - Goods and Services Tax - GST

Dear Sir, A client had constructed a govt school vide contract entered in July 2015 (i.e. after March 2015) and also constructed Police station vide contract entered in January 2016. I am aware that as per entry no. 12 of NN 25/2012 , such services were excluded from mega exemptions. Is there any recourse available to assessee to still claim exemption from service tax? Assessee was unregistered under service tax and matter has been adjudicated ex-parte and now under appeal. We are taking all legal grounds relating to validity of SCN etc but seeking opinion as to whether on merits there is any scope for exemption if the legal grounds are not accepted?