How can a "victim" contact the PO department. If they are telling lies in order to sway PO to cause more harassment to defendants. What can be done about stopping it. Can a person keep on calling PO to lie about a defendant. Also can the DA in an open case read EX Parte letters to them for the purpose of influencing the case against the defendant?

If this is a open case, the PO has no bearing on this, it is up to the DA. The PO just violates or does not violate them, then judge does a hearing.

The DA is free to look at any evidence presented.

The victim has no reason to contact the PO since that is not his issue, the victim can always talk to the DA about the case