In my opinion you don't need too much, keep your relationship with the Rollbit, as far as I know the rollbit has a pretty good reputation, it's because your withdrawal is too big, so I suggest pulling it with a small amount and do it slowly,
good luck
Op said that his account is in minus meaning it is debited already and only waiting for the withdrawal to be processed completely but that will not be processed sooner as it is not just a small amount. I can only think of that the bankroll doesn't have much (not sure how much rollbit have in their bankroll) money and if rollbit did then processing the withdrawal might cause a big problem in the bankroll which means that it will be a hard time to pay other gamblers as well. If op didn't withdraw the 31 BTC right away then op might get the BTC little by little though it won't be the same amount (withdrawal fee).