Builder doesnot return money paid for flat booking (20% value)

Hi, i booked a 2bhk flat with Royal Properties (Gitanjali Garden, Baruipur) and paid 20% advance. I was told by the builder that the project is approved by SBI for homeloans. To file application for homeloan, I was insisted to pay my share of 20%. Since it was displayed on site that the project is approved by SBI and also the SBI representative confirmed the same, I paid my share in trust. I do have all the receipts and signed contract. Later on I got a call from SBI stating that my homeloan is on hold as the building (block) in which I have booked the flat is not approved by SBI. On contacting the builder, I was assured that it is pending for some approvals from government deptts, and there's no risk. Once all approvals for this block are in place SBI will also approve. On Royal Properties owner's personal assurance, I decided to wait for approval. 1 year passed, and when one day I visited the site, I got to know that the plan for that particular block is changed and my flat's layout/size etc. will also be changed and I'll get a smaller flat. I was very upset on this information and the way things had moved till then. I told that I want to cancel the booking. The builder again insisted to book some other flat in some other project. When I finally asked them to cancel the booking and return booking amount paid by me (which I should not have paid, as 20% payment cannot be asked unless builder has all the approvals), I was told to visit their office. On various visits to their office, owner doesn't want to meet and owner and staff doesn't pick the call. I am given cheque of Rs. 1 lac, but still approx Rs.2.85 lacs is pending. Now, the behaviour of builder staff is very arrogant. They neither attend calls nor reply to emails. Personal visits are discouraged (not able to meet the concerned even after waiting). Please suggest how can I proceed in this case?