You should have told us

The Finance Department should know the answer

This must be done today

I am sorry about the mixup

We can't help with third-party claims

He must be the boss

I'll help you with this

You must refer the invoice error to the Finance Department

It is not within our ability to provide assistance of this nature

The confusion is regretted

The Finance Department is in a position to help with any queries concerning invoices

It was unfortunate that we were not aware of this issue

This is within the Finance Department's competence

This needs to be done urgently

Any assistance you need will be happily supplied

He is presumably the decision maker in this instance