Missing parcel for a client

My parcel has gone missing. It was sent from Postnet Brakpan two weeks ago. They don't seem to know where it is. I have called them numerous times and all I get is we will call you back. Also have called Postnet SA customer line, no help. This parcel was an order paid for by a client and now we absolutely have no idea how else we can get help to retrieve the missing parcel. They have promised to call back so many time and never once did.