Maintenance Amount from Builder

We are an apartment of 100 flats out of which 62 flats have been sold and 38 are unsold (with the builder i.e.) . The apartment is registered under KAO Act ,1972. Before the registration process was completed, the builder is used to pay a token amount (~ Rs 1500) each for the unsold flats while the sold flats incurred an maintenance amount from Rs 4500 till Rs 6000. After we got registered, the association demanded that the builder share the maintenance expenses equally for his 38 unsold flats as well, but the builder refused to share the expenses equally. Instead he has increased his contribution per flat to only Rs 2000. This is taking a huge toll on the existing owners as the maintenance continues to increase. Questions - Legally, isn't the builder supposed to pay the full maintenance for the unsold flats as well. Our bye laws have the provision for this but builder refuses to abide by it ? If yes, what is to be done in this case? - Does the association reserve the right to collect the pending amount (arrears) for the previous months from the new owners , as and when a flat is sold?