How can I recover a dropped table which is not in the recycle bin? I dropped a table yesterday and I want to restore it. I know that it's done with flashback but the table is not present in the recycle bin (yes it is set as ON).

So how can I restore a table that is not in the recycle bin. I am logged in as sysdba and also there are no rows neither in the dba_recyclebin nor in the user_recyclebin.
You can clone your production database to a point in time before the table was dropped, then export the table you need and import into your prod database. 
You can also try a table space point in time recovery. I tested it out a few years back, but I haven't needed to do it since.

Performing RMAN Tablespace Point-in-Time Recovery (TSPITR)