Just quit playing that site. I would seriously doubt the site is cheating you. The most likely would be two or more players colluding, and although the sites say they watch for it, I find it hard to believe they can.

Nonetheless, poker is a psychological, for you and your opponents. If some feeling is bothering you, you aren't going to be in the emotional state you need to win.

Don't worry about your bonuses, seems like you've already lost more than they are worth.