How to obtain maintenance from builder under O.C.

Dear Sir/Madam, I bought a flat in the year 2013 by a builder in a new construction property in Mumbai. The building received Occupation Certificate in April,2013. I gave first payment token in November 2013 and registered agreement of flat in December 2013. I got possession letter in December 2013 but builder charged me Maintenance for 2 years from O.C. that is from April 2013 to March 2015 and mentioned the same in agreement. During signature of agreement when i raised with builder for maintenance he said its uniform for all flats and didn't allow to change the agreement and asked to pay maintenance for full 2 years from April 2013 to March 2015. Also builder charged for VAT 1 % of agreement saying its compulsory. After learning recently i questioned builder for VAT refund as i bought the flat after O.C. after rounds of talk he agreed; simultaneously i questioned for refund of maintenance but builder replied that he has mentioned in agreement maintenance to be charged from O.C. hen