Dropped database still shows but causes errors PostgreSQL
I would guess you had open connections / transactions while you dropped the db initially and the DROP is stalled somehow.

You can get more info on databases with statistics views. For instance:

SELECT * FROM pg_stat_database WHERE datname = 'mixmobi_master';


In case you find open backend processes, you might want to shut them down like this:

SELECT pg_terminate_backend(procpid)
FROM   pg_stat_activity
WHERE  datname = 'mixmobi_master';


More about that in the manual here.

Find a safe method to drop a database under load at this related answer:


Force drop db while others may be connected