Completion certificate and occupation certificate

I have booked a flat in IRIS BAVDHAN in Pune by Skyi builder , in April 2013 with the promise of possession within 2 months. He is small scale builder who has done 4-5 residential projects. My project is single building project. The builder did not completed the work till August 2014. I have paid 95% of the payment. Now he has sent demand letter for possession with part completion certificate application and architects completion certificate. He has applied for part completion on 16-6-14 , but yet not received the completion certificate. He has completed flat, staircases and lift work. finishing in parking and landscaping, clubhouse is under construction. He is also putting in clauses that after 15 days of demand letter he will be charging 18 % interest. He has not received Occupancy certificate neither he has applied. He is denying the requirement of OC and saying he can not give any more documents. the sales and project team is trying to be faceless organization and saying we don't know about occupancy certificate including their advocate. As far as I understand without occupancy certificate I can not stay in the flat and without completion certificate builder cannot demand for possession. Will property tax be thrice if i do not have occupancy certificate ? Is the construction might having some legal problems or disputes ? I will like to have everything legally clean and clear before taking possession and occupying the flat. Kindly advice.