CREATE TABLE table_40728 ("Station" TEXT, "Local authority [a ]" TEXT, "Servedby" TEXT, "Station users 2004\\u201305" FLOAT, "Station users 2005\\u201306" FLOAT)

Which Servedby has a Local authority [a ] of thurrock, and a Station of ockendon?
SELECT "Servedby" FROM table_40728 WHERE "Local authority [a ]" = 'thurrock' AND "Station" = 'ockendon'
SELECT "Servedby" FROM "table_40728" WHERE "Local authority [a ]" = 'thurrock' AND "Station" = 'ockendon'