1. If the brochure or any agreement states that you are required to pay 40% of the price of the flat towards booking amount then you were supposed to pay the said 40%. If it was told only and there is nothing in wrtiting, then you can also very well claim that your were told to pay 20% of the price towards booking amount,
2. However, if the builder and/or its agent has called for booking of flats to be constructed illegally supressing the fact that no sanction of the building/project plan has yet been obtained by them which is a must for condtucting a building/project, then their entire act of collecting booking amount, be it 40% or 20%, is illegal and can be challenged before the appropriate Forum/Court,
3. You can file a complaint case alleging deficiency in service and unfair business practice claiming the said refund, interest, damage amd cost as suggested in my earlier post.