Consumer Redressal

I bought an apartment in Vatika City in April 2010 in re-sale. I bought the flat for approx 65 lacs. At the time of transfer, I submitted all the documents to Vatika City and paid 61 lac to seller and retained 4 lacs for Vatika for final payment at the time of possession. The calculation of 4 lac pending to Vatika was done by vatika and given to me at the time of submitting the documents for transfer. After couple of months, Vatika gave me new builder buyer agreement with wrong calculation as 9 lacs for final payment at possession instead of 4 lacs mentioned by Vatika at the time of transfer. But after I raised the concern, Vatika recalculated the amount to 4 lacs and I paid the same at the time of final payment of possession. Now after 3 years when we want NOC from Vatika for registration of our flat, they are again asking us to pay rest of the amount (9 lacs - 4 lacs) to give NOC. They are saying that they did mistake at the time of transfer and possession but now i have to pay