Illegal Cancellation of Flat by Builder

Sir, I had purchased flat at sector 45 Noida by signing a Allotment Letter on June 2013. I had paid 95% of payment till april 2014 with a promised to deliver the flat by april 2015. Balance 5% of the payment was to be made at the Offer Of Possession. On 30th November 2015 builder issued Final Demand Letter without having Occupation Certificate for the Project. Occupation certificate for the group housing project was received on 20th May 2016. Builder again demanded that I should make the payment as per Final Demand Letter dated 30.11.2015 and to give minimum 60 days of fit out period to make the flat ready once I clear all the dues in advance. This particular demand from the builder was Illegal as according to the Allotment Letter I was supposed to make the balance 5% of the payment only on Offer of Possession. Offer of possession was only possible when the flat was ready in all respect (presently flat is in raw condition) and they are in position to register the flat and then only they could give possession. Even though builder has received OC on 20th May till date not even a single flat has been registered by the authority. Yesterday they have send me notice that in the absence of making the payments they have cancelled my allotment. Its a day light robbery. they have taken all my money and now they are not even given me the flat. All I did was I stood by the Clause of Allotment Letter which states that I have to make the balance of Payment at OFFER OF POSSESSION. Please advise. Thanks.