An invoice and a statement are routinely confused and one of them should never be paid from. An invoice is a claim for a specific supply, with lines that can be matched against an order and a receipt. A statement is a supplier's list of what they believe is outstanding, with no line detail and no way to verify anything.
What an invoice is
A claim for payment for a specific supply, with a unique number, lines with quantities and prices, tax, a total and terms. It can be matched against the purchase order and the goods receipt, which is what lets it be verified. Every control in payables is built around this document and what can be compared with it.
What a statement is
A periodic list from the supplier of invoices they believe are unpaid, with numbers and amounts and no line detail. It is a reconciliation tool: comparing it against your record finds invoices they raised that you never received, credits not applied, and payments allocated to the wrong item. It is genuinely useful for that.
Why paying from one produces duplicates
A statement may list invoices you have already paid but which have not yet cleared on their side, and invoices you never received and therefore never verified. Paying from it means paying without the underlying document, without a match and without knowing whether the goods arrived. It is a reliable route to duplicate payment.
How to use statements properly
Reconcile them monthly for high-volume suppliers and periodically for the rest, and treat every difference as a question rather than an instruction. Invoices on the statement that you do not hold should be requested and then processed normally, through the same validation and matching as anything else.
Questions people ask about invoice vs statement
What if a supplier only sends statements?
Ask for the invoices. A statement is not a substitute, and processing without the underlying document removes every verification step you have.
How often should statements be reconciled?
Monthly for your largest suppliers by document count, and periodically for the rest, with the rule based on spend.
What do reconciliations usually find?
Invoices you never received, credits not applied and payments allocated to the wrong invoice. All three are cheaper to find monthly than annually.