Non Acquisition of Flat

I want legal advice on non acquisition of Flat. There was a upcoming project in jabalpur where I booked the flat in 2011. As per agreement I made all my payments by post dated cheques which was completed by sept2012. As per the agreement the builder said to do registry within 17 to 24 months from date of completion of payment. But when I recently reached to him he himself stroked down the 17-24 month clause and changed it to 36 to 48 months. At the time of agreement the building was supposed to be of 10 floors but recently he told that its now of 6 floors with my flat booked on 5th floor. As of now, the progress is not much. When I asked about interest on the amount paid the builder refused that there is no such mention in the agreement (thats true as I was not aware of nitty gritty of agreements so its not written there). I want legal advice on what can I do at this stage. Do I have any say in it or just have to keep waiting for and if he completes the building or is there any mechanism through I can claim interest on paid amount or any other type of redressal.