Vastu Vihar — builder is not completing the project on time

Address:

1st Floor, Mahuli Tower, K.G Road, Ara Road, Arrah, Bihar 802301, Bhojpur, Bihar

I have booked a flat having details jayanti 22 kaymnagar ph - 02, arrah in nov 2015. Still the construction is not get completed. I have paid almost 80% of the amount till now and took the loan and started paying back to bank as well. I am willing to pay the builder but they are not completing the project on time that is why i am not paying the full amount. It has been almost 4 years passed but builder is not picking my call from last couple of months whenever required. I am doing job @hyderabad and having some medical issue with my father. So i do not have time to go there and spent enough time for the completion the project.
This is pathetic service provided by the company. Now my concern is can i file case against the builder at the moment or can you please any alternative suggestions?