To get money back from builder due to non-possession of flat

Hello Sir, I had invested in property in April 2011 in Badlapur near to Railway station As per the registered agreement, the possession was to be given by April 2012. I had taken home loan of 21 lakhs from Bank. I received regular demand draft to pay money to builder as and when the slab work was progressing. But due to some issue of NOC clearance from the Railway authorities - the possession of flat was delayed every year. It has been now 6 years and the NOC is still not cleared and there is no flat available. Hence, now in 2017- we asked the builder to give back the amount invested in the flat. The builder has suggested that - We should cancel the property agreement and during which he will provide the Cheques of all the amount paid till date. Could you please help me know if there is any such procedure to cancel the agreement and get the money back from the builder. Please help me with this issue - if cancellation of agreement will not pose any problem. Also, I am outside India for work related...and intend to give Power of attorney to my Uncle. Could you please also suggest what kind of Power of attorney to be given to Uncle so that I am assured that I get all the money in my name? Thank you