Is POA required for refund of tentative money paid?

Im an Indian Armed Forces Officer presently on deputation to US. My brother in law booked an apartment in Greater Noida west with Sikka group on my behalf in 2015 and till date I haven't signed any Builder Buyer Agreement or any legal document with the builder. Till Oct 2016 I have paid more than 13 Lakh towards the property as an tentative amount. On investigation, found that the builder has not done any construction for the said project from last 2 years and even changed the name of project without informing the allottees which is the case of fraud. Accordingly have been requesting builder to refund my dues paid from last 6 months, the builder agreed and confirmed would pay the amount in 4 installments in 90 days and without any interest after GPA signed and notarized in US authorizing my brother in law to sign refund papers is given to builder. I contested that since there is no legal document or Builder Buyer agreement signed with the builder which binds me for providing an POA for refunding the money to my account and authorizing my brother in law signed all papers. I mentioned that i can provide an authorization letter to authorize my brother in law for signing all refund papers, but they are just delaying and asking for POA. Seek your valuable advise as to what would be best course of action in this case to make builder refund my hard earned money without delays at the earliest and make them pay for case of fraud and harassment to me. Thanks Gavi Kumar Major