Notary without registration

My father's land is in Nagpur and the local authority of Nagpur NIT had not been giving sanction for Land regularisation for more than 15 years because as per NIT two societies layout are overlapping and to solve this one builder had proposed the plan to plot owners of society. He said he would get regularised the land and get sanction for Flat scheme from NIT and build apartment and handover one flat each land owner. Builder had taken signature of all land owner on power of attorney which was written on 500 Stamp paper and not registered to carry out all regularization and sanction of land on behalf of all land owner. He had been said that he would handover the flat within 3 years but now it has been 4 years neither he developed nor regularised from NIT. My father had sent three notice to builder regarding cancellation of power of attorney but he never replied. Please suggests whether builder can misuse the power of attorney.