May i go to consumer court if the load factor is around 65%

Dear Sir/Madam, Greetings for the day. I booked a flat from a private builder in March 2014. The super area of the flat as mentioned by the builder is 1008 sq. ft. in the builder buyer agreement. The cost of the flat was Rs. 21,00,000. The flat was sold on the basis of super area. I paid Rs. 6,30,000 in the first three months. Rest of the amount was to be paid after offer of posession. I received an offer of Posession from the builder on 10th November 2014 while the flat was not ready. Issue: 1. When i visited the construction site and measured the carpet area it was just around 540 sq. ft and the covered area was around 600 sq. ft. which shows a load factor of around 65%. 2. At this i talked to the builder and asked him to provide me the load factor, calculation sheet and the map approved by the competent authority. But the builder get annoyed with me and send me a final notice for payment on 16th January and asked me to make balance payment till 20th January 2015. 3. I have got my loan sanctioned already from GIC housing finance limited which is the only organisation who has approved the project and they have told the same to my builder that my loan is sanctioned. 4. Now my builder has sent me a legal notice and has asked me to make the balance payment along with an interest @24% p.a. from 15th december till the date of actual payment. Query: 1. How to reply this notice first so that i am relieved of this interest in future. 2. May i go to consumer court against the builder if so much is the load factor. 3. How to get load factor, calculation sheet and map from the builder. Kind Regards, Arun Agrawal