There's a sad truth about dealing with suppliers - most will send you incorrect invoices at one time or another. When they do, ensure you follow the steps below to resolve the issue and receive credits from the supplier:
Check Contract Terms and Pay Required Amount
What are the terms in the contract? If you are allowed to, pay only the undisputed portion of the contract. Follow all contract clauses to avoid penalties.
File an Official Complaint and Follow-Up as Necessary
Providers have formal processes for filing complaints. File promptly and be sure to follow the rules exactly. In addition, periodically follow-up with the provider until a resolution is achieved.
Monitor Accounts for Action
Just because the supplier agreed to a credit does not mean that the credit will be correctly applied to an invoice. Set-up reminders in your calendar to check invoices thoroughly for expected credits.