This isn't a guarantee... but if you CC your email correspondence to ZipZap as well... they (Bitinstant) tend to respond faster... at least that was the case with my outstanding transfers (5 at one point... all paid up).  It's kind of like tapping on someone's throat with a pencil point while you're 'discussing' something, they tend to give more importance to what you're saying.... because if there is no relationship with Zipzap, there's no Bitinstant (in its current form anyway).