It was because he was only paying me for 18 posts and not 25. Then he thought I didn't meet the 25/week deadline and kicked me from the campaign based on that false assumption from his error. The pay increase I mentioned was the increase from 18 to 25 posts.
Long story short, even if the manager committed error, he might have already removed you from the campaign next week itself. Tell me how are you assuming that you lose $900? Are you just making an assumption that you'd have remained in the campaign till its end? What if you'd have been removed next week itself for no reason based on the campaign manager's policy? Either you've gone totally insane or you're fighting just for the sake of the missed payment of those 7 posts. Getting into a campaign doesn't really guarantee your long term relationship with the same, you're not entitled to remain in a campaign till its end as each campaign has a policy to remove a user, they believe, doesn't fit to their requirements in any means and/or for any reasons.