This is not the right section for discussing scams or scam accusations. You should move this thread to:
Scam Accusations. There's an option to do that in the lower left corner of the screen when viewing this thread.
5. One week later he change rule and all participants of the bounty campaign have to perform additional work again. But at that time at most of participants work has been already completely performed.
If you've claimed/joined the bounty with predetermined rules/conditions, and you've completed said conditions then you have earned whatever was *promised* at the time. Changing these conditions afterwards is shady at best / an outright scam.