Problems with query rewrite and materialized views

Hi,
I've got a problem to use query rewrite with a materialized view I created.
When I write a query which is different than the query of the materialized view, the execution doesn't use the materialized view but the tables.
My database is in choose mode, and I have the 'enabled_query_rewrite=true' in the init.ora file.
What should I do?

grant QUERY REWRITE
grant GLOBAL QUERY REWRITE

I've evere tried it but it didn't solved my problem