How to cancel AP invoice which already matched with PO

Hi,

If an R12 AP invoice already matched with PO, what is the correct process to cancel the invoice so that the billed amount will recalculate correctly in PO level.

We facing couple of issue with PO, user have cancelled the invoice but the billed quantity and billed amount is not captured correctly after invoice cancelled in AP. In PO level, it showing over billed.

Thanks
Renish