Worth having a standard procedure for this, because it happens more than you would think and the instinct to treat it as an error is usually wrong.

The situation: you are reviewing a set of accounts and a charge shows up that was not there the month before. Same cycle across every account. Some new surcharge, adjustment, or component of an existing charge restated on a different basis.

The order I work it.

First, is it arithmetically correct as billed? Recompute it against the printed rate and determinant. If it recomputes, you do not have a billing error and you should stop framing it as one.

Second, is it authorized? There should be a filed tariff leaf and, behind that, a commission order. Both are public. If you cannot find either, that is the finding, and it is a much stronger one than a rounding argument.

Third, is the rate correct and consistently applied? Compare across accounts and across cycles. A surcharge that varies cycle to cycle without an obvious reconciliation mechanism is worth a question.

Fourth, is there an offsetting reduction elsewhere on the bill? Restructures frequently move recovery from one basis to another rather than adding cost. If the total is roughly flat, your client has a rate design issue, not an overcharge.

Fifth, is there a true-up? If the component reconciles later, today's number is provisional.