Unjustified Charges of Interest and other at possession !

I have bought 1895 sqft flat in 2012 in Noida from reputed builder under CLP plan, I have following problems : 1. Builder raised demand of multiple milestones together and when investigated found them not be complete. I submitted photos and video to builder and sent them more than 10 emails denying wrong demand. But builder never gave me any answer. 2. They then offered me possession while nothing was complete on site and project completion certificated was not granted by NOIDA authority and it was not at all livable. 3. Now again after 10 months they sent me demand and offered me to complete and give me possession and i was ready to pay and take possession, but when i asked them to send me list of all payments to be paid to take possession, they added 3 lacs of interest for delay of my payment which was against wrong demand and to avoid their delay in possession penalty. Now, I have few questions: 1. Shall I make payments and protest the interest payment or shall I pay and then file legal case? 2. can i just make payment as per contract w/o interest and apply in court to get me possession as they will not give possession. 3. can i get income tax benefit without getting possession as dispute will be there after case?