Me: Your bills are confusing, the amount due this period isn't really the amount due.
Her: Actually it is, if you only send in the amount due from the previous period, it's right.
Me: When I pay my bill, I usually round up to the nearest dollar, or pay ahead for a package that I sent, but wasn't invoiced yet.
Her: You shouldn't do that, our systems don't support negative balances.
Me: That's interesting, because I have overpaid before, and it was deducted from the next bill.
Her: That's because we have a team that takes the over-paid amount and counts it as a refund voucher.
Me: Which then gets applied to my bill?
Her: Umm, yes.
Me: So how is that different than a credit?
Her: I guess it's not, but please just pay the 'Amount due this period', and there won't be a problem.
Me: I didn't think there was a problem.
Her: Is there anything else I can help you with?
Me: Nope, thanks
Bewildering that a company as large as UPS doesn't have credits, yet they do. I was very confused.