If you believe your invoice is incorrect, you can raise a dispute on it. Once you log into MyFinance, find the invoice you wish to dispute and select it (tick box). In the bottom bar, you will see the total invoice amount on the left, and some icons on the right.
Select the 'Dispute' icon.

This will take you to a new page, where you can review your selection, and select a Dispute Reason from the drop down list. You may be required to provide more information about what is incorrect, and you can attach supporting documents if you wish to.
Then click on 'Continue' to complete the Dispute submission.