Mantri Developers — delayed possession

Address:

Manyata Tech Park, Bangalore, Karnataka

Mantri energia was promised to be delivered by dec 2018. Later they informed us that it’s been delayed to 2019. The earlier date itself was 1.5 years delayed it seems.
When we enquired in their office, we were mistreated by their staff. We don’t even get the status report. I don’t know whether they will deliver the flat or not. I am not sure what action should be taken to treat these guys with some lessons.