Possession Of The Flat Is Delayed

I have purchased a builder flat in June 19 which was under construction. The agreement was that possession will be given in 18 months starting from date of agreement say around in Dec-20. But I have not got the possession yet. Builder says it is due to lock down due to Covid 19. But looking at the building it looks like it will take months to complete work. This building is not in society and I think does not even fall into RERA. What to do if possession is delayed. If I go into litigation is there any relief possible in a decent amont of time. Can I file a suite against the dealer who was involved this dealing, as payment was made to him online. Phone call recordings also available.