Prepaid Utilization

Hello,

Wondering what could be the best approach to proceed in the following scenario: Prepaid contract has been utilized in full - all prepaid events are depleted. Later, credit transactions (expenses) hit the project and negative BILs are created. Utilizing those credit lines generates a credit invoice (utilization process doesn't roll backward). What can be done in order to be able to process a refund for the total credit amount without messing up accounting entries. I know the reasons why backward utilization doesn't happen after prepaid is depleted.

Thank you,

Armand