1. If you have taken possession of same builder can ask.for maintenance amount if not you are not liable further you can issue legal notice to complete the work if there is delay in work or further fails complete work consumer complaint can be filed.
If there is change in plans approved deny paying same if no prior permission is obtained for same.
File a consumer complaint against builder and recover the cost.
Donot take possession without proper.amenities and registration and demand from the builder.damages.