Delayed & Poor quality construction still asking for possession

Jurisdiction Ahmedabad * Builder delayed possession from dec 2012 (Promised) to July 2016 (Registry Date). * Asking for compensation he denied based on non-availability of labour. * Made changes in layout witout consent. * Changed the tile size from 3feet (mentioned in sale deed) to 2.75 feet without consent. * Poor quality of construction has been provided Builder said all quality defects are snags and will be rectified. After asking to replace tiles their representatives denied & said that tiles with such dimentions are not available in market. Also denied written solution to other mentioned 40 points for correction (on this newly constructed flat). Instead made a meeting with their lawyer stating all corrections are in discreetion of buider. Today a legal notice has been sent saying if the possession is not taken before 20th then it will be deemed possession and builder will not hold any responsibility of any damages. Kindly suggest next action. Note: Registry of flat has been done.