Hello,
not sure I follow the whole problem, hence, allow me a few questions. It usually helps to understand.
You had won something while playing with the bonus, but after some time, the bonus and the winnings were gone. Usually, the best way to get a direct explanation is to contact the casino. We can start speculating just now, but there are far too many possibilities, such as:
has the bonus expired?
have you submitted a withdrawal request?
have you met all bonus requirements (specifically wagering)?
have you played according to the rules the whole time? (max bet rule, forbidden games, and so on)
Additionally, your winnings seemed to have waned, but you are still convinced the games are rigged. I bet you expected higher winnings, right? Frankly, this feeling is quite normal. Just lower your expectations; you might feel better. I imagine how it sounds, but licensed casinos just can't alter the games on any occasion.