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).
Right, and they would have some justification of forfeiting winnings had OP used a bonus on this deposit cycle, but OP claims that they did not and Bitstarz did not refute this. Rather, they chose to victimize themselves.
They are trying to argue about abusing the bonuses - which are -ev by the way, even without the completely ridiculous maximum bet T&C - when it has nothing to do with what OP experienced.