I know this is extremely embarrasing.
But technically the bonus has rules and one of them was that you cannot claim a bonus with any baalnce in the account.
The only point here is that of "good faith", which is not easy to request strongly.
I would advice to sumbit a
PAB with casinomeister here.
http://www.casinomeister.com/problems.php
He may work things out for you.
Since your point with them is of good faith and not of formal obligation from their side, I would advice not to make yourself their enemy.