House not handed over

We bought a Flat at Khyban-e-Amin (Sahir Associates) in 2010, and full payment was completely paid 9 years ago. But they haven't completed construction yet and are not handing over the house. It has already been 9 years since the full payment. They are not even providing the possession letter. Other than that, they also changed the flat location(block) from N block to P block without any valid reason.