Possession in 2008 but no completion till 2017

Hi, I live in PMC and bought property in 2008 (Sukhsagar Nagar, Katraj, Pune). As I was paying rent, I took possession by the builder in 2008 where completion certificate was not received. The builder has given me possession letter and has taken in written that I am happy with the work and have no complaints about the property. Moreover, the 3rd floor of the building has still (as on 2017) has not got permission but he sold those flats to people. only first 2 floors are legal. We are following up but neither he visits, nor he takes any responsibility. He always says that he has got more permission, he will build and complete the building then. It has been now 9 years we are listening to the same. People contribute on their own for monthly maintenance. 1. Who has the responsibility about the building in this case? 2. Whether completion can be achieved without builder's permissions directly? 3. What can be done in this case? 4. Is filing a case an appropriate option? If so, how many years it may take?