Caste validity certificate

I have completed my graduation 3years back and after that i was working but now i want to pursue MBA. So as i belong to SC category i want to avail the reservation quota, i have the caste certificate and all other valid documents, but as being an ex student neither my college is providing me covering letter which states my caste (FORM 15A Declartion) nor the validity officers are understanding my situation and asking me to provide 15A declaration. I also explained them if you want i can attach the resgistration copy of online form for MAHCET exam but they are asking me to also attached the hall ticket and score card of the exam, i dont have any problem to do so but score card will be released too late after the exam and also the document verification begins just within few days after the declaration of result, so i wont able to get my certificate or even receipt for the same and i have to give up my quota and have to apply under open category which i cant afford because of being from a lower middle class family. so please help me regarding this what can i do in such scenario's.