It occurred to me so many times that even after flagging a question which is an exact duplicate or may be not a real question at all, moderators sometimes don't close the question.
What are my options in that situation? Can I escalate it?
You provided a link in the comment of the original question. It's not that moderators declined your flags, we hadn't seen it yet. There are currently 202 open flags waiting for moderator review on the site. About 20 minutes ago, there were over 300. Yours was one of those 300. It would have probably been resolved in a few hours.
You flagged the question two hours ago (although it says 9:33:10 Z), and wrote this post an hour ago (however, the timestamp is 10:28:01 Z). We need a little more lead time than that.
Give us time to work for you. Flagging does not result in an instantaneous response from a moderator. Sometimes it can be hours before we get to flags. Our average handling time is a little over 5 hours for this month. That's a good lead time.
In this particular case, we hadn't seen the flag yet, so it's not as if we declined to handle the post.
If and when you do see a declined flag when flagging a duplicate, then you know that the moderator who reviewed it decided to decline it. Even when a moderator declines a flag, that doesn't stop the community from taking action.
I went ahead and resolved the flag. Keep on Keepin' on.
If a moderator looks at it and decides that the two aren't exact duplicates, and the folks reviewing close votes don't think it is an exact duplicate - perhaps it isn't an exact duplicate after all?
Why the rush to close it off? It will eventually get closed or closed as a duplicate. If you really feel the need to intervene, why not just leave a comment saying that it is a duplicate and a link to the question that you think it is a duplicate of. (This will give high rep users a good incentive to look at your link - and if they agree with you, cast a close vote - Doing this could close the question much quicker than waiting for a moderator to get through their list and get to your flag).