As far as I understand this concern, I think it's not right to call it as an "abused" since he is using only one account and he just continue to play his game to claim that bonus. If the bonus can't be claim once the original deposit was depleted, the bonus should be voided at the moment he lose the last spin and automatically restart the bonus counter. But yet it continues by the time he deposit again.

AFAIK, the error was on your bonus structure tho.

PS: I'm not so sure about this issue. Correct me If I'm wrong if ever I misunderstood the issue here.