Billing errors are mistakes in the way a statement calculates, labels, or carries forward what you owe. They can be small, such as a fee that appears twice, or larger, such as a cancelled service that keeps billing after it should have stopped. The hard part is that many errors look similar to ordinary bill changes unless you know what to compare.
A careful review starts with the basics: the billing period, previous balance, payments received, recurring charges, usage charges, one-time charges, credits, and taxes. Each section answers a different question. If the billing period is longer than usual, a higher total may be expected. If a new one-time charge appears, it should match a real event. If a credit is missing, the current balance can be wrong even when the total looks plausible.
Use this topic as a starting point for learning how to spot billing mistakes before you pay. The related guides explain step-by-step review habits, and the linked terms define common line items that often need a second look.