In this scenario, OP was not trying to get as many bonuses as possible, were they?
In this scenario, their deposit had no bonus terms associated thereof and they were betting like any other regular player.
As I understand it, OP has created multiple accounts with similar email addresses looking more or less the same, indicating that he was trying to get the bonus on all of them (all but the one he was "caught" with). I'm not sure if I missed something, but if I'm not, this is the only thing Bitstarz might have a valid point with. However, this does not change that:
You are blatantly stealing.
Which is, plain and simple, unacceptable. As a casino, you have to expect such behavior (hell, you're making your money from people who at least part of them are addicted to gambling! What do you expect, for fuck's sake!)
You have the technology to identify and ban them. There is no reason on earth you're eligible to keep their deposits.