How do I retrieve a credit balance (of unspent cash, not minutes, texts or data) from an account when I have ported the phone number to another carrier?

Specifically: I had a small cash balance - should be about $19 or $20 - in a 2Degrees prepay account.  I ported the phone # to Vodafone (because shortly I'll need to keep the same number while roaming in countries where 2Degrees doesn't seem to offer roaming packages).

I'd like to get the cash balance back, but I'd also be quite happy to have it transferred to my other, continuing, 2Degrees prepay account.

When I login to the account with the now ported-away number, though, it says there is no number associated with the account (fair enough), and I can't see how to find my cash balance.  

I understand fully that the accumulated minutes, texts and data allowance must be lost, but the cash ought not to be forfeited.