how to Cancel a PO line

 Hi,

we are working in oracle applications 11i. we have a PO with one line that was approved and received and then invoiced and pid from the system.

The PO now is in  the status  of requires reapproval. and the accounts are not affected correcly because the item code is assigned a wrong unit of meaure that does not match the quantities of the po line.

There is an urgent need to cancel this po line. is this possible?and how ?any workarounds??  any thing???