Runwal Group — Wrong commitment given while booking flat

Hii
We have booked a flat on runwal my city where people are already staying. While booking we have told already to sushmita that we need to do stamp duty registration on 7 of september due to our auspicious date. She have given confirmation. But suddenly we have got to know that they are going to do stamp duty on end of oct. Which is not acceptable. Why wrong commitment is given while booking. We need our refund back or else arrange stamp duty on 7 sep.