Builder increased maintenance charges after society formation

Hi, I purchased flat in Oct 2017 and paid advance maintenance to builder through investor (second agreement) for one year. Society formation was done in Apr 2018. In the first meeting builder promised to refund balance advance maintenances to society. But now when society approached builder, he is saying that he will not refund it to society and will talk to individual owners. Accordingly, builder sent letters to owners and hiked maintenance changes by 850 per month and accordingly adjusted balance and either showed refund from builder or demanded (depending upon calculations). Now I have following questions, 1. Can builder communicate and increase maintenance changes post facto and charge it to owners after society formation? 2. Society is charging me maintenance charges from Apr 2018!!!! How to deal with society. Why should I pay to builder and society as well?? 3. What are channels which I can explore to find out legal solution without case......Do RERA has any provision to deal with it Please suggest