I bought a flat 4 years back which is due for more than 2.5 years as per the contract. The penalty c

I bought a flat 4 years back which is due for more than 2.5 years as per the contract. The penalty clause for delay as per agreement seems to be only on paper. Recently I received a letter for completing some work in my flat from the builder's office. I visited area thrice and everytime I was told that I cannot see my flat for some reason or the other. I sent mails and letters to the Builder to allow me to see my flat before I make payment but there is no response from them till date. What can I do in this case?