Hello, my account has been flagged since 15 march, and i am not getting any pop up ads and also brave news ads rewards.
What should i Do?
How long did it take for your account to unflagged?
Linked below is a post from a moderator about flagged accounts. You can submit the request form linked in the post. You may get a response since your account has been flagged for such a long time. Hope your issue is resolved! 
Your fix is a rewards scam and will likely result in the users suspension if implemented.
you know one thing, yesterday in the morning i reinstalled brave browser and in the evening i got a mail from brave that your account has been unflagged now whatever your payments are awaited will be completed, and ads will be continues.