As it is now, if we (your customers) get credits, as far as we can tell they are just floating out there somewhere with an implied promise to be used because they are not documented on our bill. When you post a bill for a customer it should be what they owe and itemize everything including any credits applied to it. This is standard business practice. I use Quicken and usually post my bills early (as soon as I know what they are) but with Ting I can't do that if I have credits because they bill doesn't show them. Credits are a part of the bill so they need to be listed. Doing this will also facilitate historical questions for your customers.
Make things less confusing for your customers