Iv been blocked from Cassava bingo sites for winning?

Hi I am a member of many of the bingo sites run by Cassava. They run Costa, Cheeky, Singbingo, Moon bingo, Wink, Think 888 Tasty Redbus Gossip etc.... I have always deposited a lot of money on these sites but I also withdraw as soon as I am able to. I probably withdraw about the same as I deposit but no more. I had an email off Cassava the other day saying my accounts have all been blocked as I was apparantly abusing their bonuses? Rubbish as when you win they take the bonus off you anyway. They owe me about �120 in pending withdrawels wich they informed me I would not be getting even though they gladly took the �140 out of my bank in deposits! Can they do this? Has this happened to anybody else and if so what can I do about it?. Also who regulates these sites? Any advice would be greatfully recieved thanks.