Cancellation of flat booking and refund of 10% booking amount

I bought a flat in 2014 by paying 10% of the flat cost. At the time of purchase, I was told by the developer’s agent that the project will have club house, school, mall, and lots of other amenities. I have all of these in email chain with the agent. The project was supposed to be a township type project. The buildings are constructed and builder have started giving the possession from Aug last year, but no club house, mall, school, and other amenities are developed. The product that’s getting delivered is not the same which was sold to me, and so I am not paying the balance 90% to the developer and asking him to cancel the booking and refund my money. Initial cancellation request was made in Jul-Aug last year over the phone but after no action from the developer side, from Sept-Oct last year I started writing to them emails. The developer has been very slow and after multiple follow ups since then he has finally reverted now with the cancellation process which is quite lengthy which includes indemnity on stamp pager, bank verification, agent consents, etc and to my view not warranted. And instead of refund of my 10% booking amount, he is asking me to pay big amount for cancellation which includes interest on balance 90%, GST, maintenance, etc. The project is in Panvel and is registered under RERA. I have not signed any legal agreement with the developer. Please can you advise whether I have any recourse to get the refund? If yes, how should I proceed? If no, what’s the best way to get out of this deal? Thanks