I know that I cannot pay out a bonus. But ALL of my winnings have been raided, because I made some bets above 4 Dollars!

I did not know about the 4 dollars, it's somewhere in the terms. A fair systems would let people know or even pop up a message "Hey, you are betting more than 4 dollars, you will loose all of your winnings if you do so."

That would be fair. Everything else is a scam in my eyes. At the end I lost all of my winnings, even the ones I played with less than 4 dollars. (I played with 5 dollars, that's correct).

So to me this here is just a bonus scam and this is it.