About Payment of Interest for a Falt Allotted in Greater Noida

Dear Sir, My name is Sourabh Joshi I have been allotted a Flat 29.76 sq mtr sector MU II in Greater Noida by Greater Noida Industrial Development Authority. The cost of Flat is 863000/- in which Rs. 80000/- has been paid as registration money. After the draw result we paid 179800/- as allotment money. From dated 02.05.2014 there is 14 installment of Rs. 43150/- half yearly for balance amount of Rs. 604000/-. The Possession has not been receive till today. The Authority is charging the interest @ 12% p.a on balance amount of Rs. 604000/- thus My installment become amount to Rs. 79396/- after addition of Interest Rs. 36246/-. I want to know that why they are charging such interest while they didn't give any benefit to me for that amount. I think I should pay interest after getting the possession of flat only on balance amount at the time of Possession. The installment which I have paid before the possession should be treated as advance. I request you Sir please give me some advice that my point is correct or there is any provision in law in respect of this. Thanks Regards Sourabh Joshi